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 $203.28   10.309%   $224.2361   $224.24   $224.25   $224.20  
  Purchase #2 $235.74   11.242%   $262.2419   $262.24   $262.25   $262.20  
  Purchase #3 $127.77   3.142%   $131.7845   $131.78   $131.80   $131.80  
  Purchase #4 $50.98   6.144%   $54.1122   $54.11   $54.10   $54.10  
  Purchase #5 $166.96   5.591%   $176.2947   $176.29   $176.30   $176.30  
  Purchase #6 $189.92   4.702%   $198.85   $198.85   $198.85   $198.90  
  Purchase #7 $144.31   7.867%   $155.6629   $155.66   $155.65   $155.70  
  7 purchase totals = $1,118.96       $1,203.1823   $1,203.17   $1,203.20   $1,203.20