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 $246.86   10.283%   $272.2446   $272.24   $272.25   $272.20  
  Purchase #2 $234.77   5.721%   $248.2012   $248.20   $248.20   $248.20  
  Purchase #3 $184.96   9.200%   $201.9763   $201.98   $202.00   $202.00  
  Purchase #4 $208.41   5.394%   $219.6516   $219.65   $219.65   $219.70  
  Purchase #5 $159.99   7.294%   $171.6597   $171.66   $171.65   $171.70  
  Purchase #6 $139.45   12.295%   $156.5954   $156.60   $156.60   $156.60  
  Purchase #7 $213.45   9.201%   $233.0895   $233.09   $233.10   $233.10  
  7 purchase totals = $1,387.89       $1,503.4183   $1,503.42   $1,503.45   $1,503.50