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 $66.82   12.603%   $75.2413   $75.24   $75.25   $75.20  
  Purchase #2 $150.92   5.116%   $158.6411   $158.64   $158.65   $158.60  
  Purchase #3 $116.92   8.354%   $126.6875   $126.69   $126.70   $126.70  
  Purchase #4 $187.34   4.154%   $195.1221   $195.12   $195.10   $195.10  
  Purchase #5 $197.30   4.809%   $206.7882   $206.79   $206.80   $206.80  
  Purchase #6 $85.98   11.281%   $95.6794   $95.68   $95.70   $95.70  
  Purchase #7 $57.72   3.836%   $59.9341   $59.93   $59.95   $59.90  
  7 purchase totals = $863.00       $918.0937   $918.09   $918.15   $918.00