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 $46.71   11.555%   $52.1073   $52.11   $52.10   $52.10  
  Purchase #2 $183.84   12.662%   $207.1178   $207.12   $207.10   $207.10  
  Purchase #3 $244.68   9.484%   $267.8855   $267.89   $267.90   $267.90  
  Purchase #4 $46.90   6.573%   $49.9827   $49.98   $50.00   $50.00  
  Purchase #5 $56.95   3.545%   $58.9689   $58.97   $58.95   $59.00  
  Purchase #6 $149.87   5.619%   $158.2912   $158.29   $158.30   $158.30  
  Purchase #7 $151.79   7.237%   $162.775   $162.78   $162.80   $162.80  
  7 purchase totals = $880.74       $957.1284   $957.14   $957.15   $957.20