Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.99   13.225%   $281.9189   $281.92   $281.90   $281.90  
  Purchase #2 $176.98   4.367%   $184.7087   $184.71   $184.70   $184.70  
  Purchase #3 $209.74   10.855%   $232.5073   $232.51   $232.50   $232.50  
  Purchase #4 $150.25   5.303%   $158.2178   $158.22   $158.20   $158.20  
  Purchase #5 $238.59   11.566%   $266.1853   $266.19   $266.20   $266.20  
  Purchase #6 $193.42   7.474%   $207.8762   $207.88   $207.90   $207.90  
  Purchase #7 $125.98   8.148%   $136.2449   $136.24   $136.25   $136.20  
  7 purchase totals = $1,343.95       $1,467.6591   $1,467.67   $1,467.65   $1,467.60