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 $53.42   12.664%   $60.1851   $60.19   $60.20   $60.20  
  Purchase #2 $72.43   13.687%   $82.3435   $82.34   $82.35   $82.30  
  Purchase #3 $178.66   11.826%   $199.7883   $199.79   $199.80   $199.80  
  Purchase #4 $161.61   12.723%   $182.1716   $182.17   $182.15   $182.20  
  Purchase #5 $66.72   12.706%   $75.1974   $75.20   $75.20   $75.20  
  Purchase #6 $194.99   10.806%   $216.0606   $216.06   $216.05   $216.10  
  Purchase #7 $151.56   6.361%   $161.2007   $161.20   $161.20   $161.20  
  7 purchase totals = $879.39       $976.9472   $976.95   $976.95   $977.00