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 $37.50   11.719%   $41.8946   $41.89   $41.90   $41.90  
  Purchase #2 $159.96   13.849%   $182.1129   $182.11   $182.10   $182.10  
  Purchase #3 $244.37   3.843%   $253.7611   $253.76   $253.75   $253.80  
  Purchase #4 $59.86   3.537%   $61.9772   $61.98   $62.00   $62.00  
  Purchase #5 $207.86   9.355%   $227.3053   $227.31   $227.30   $227.30  
  Purchase #6 $135.59   3.500%   $140.3357   $140.34   $140.35   $140.30  
  Purchase #7 $21.54   11.368%   $23.9887   $23.99   $24.00   $24.00  
  7 purchase totals = $866.68       $931.3755   $931.38   $931.40   $931.40