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 $34.66   3.610%   $35.9112   $35.91   $35.90   $35.90  
  Purchase #2 $144.93   5.719%   $153.2185   $153.22   $153.20   $153.20  
  Purchase #3 $175.45   10.740%   $194.2933   $194.29   $194.30   $194.30  
  Purchase #4 $29.54   9.234%   $32.2677   $32.27   $32.25   $32.30  
  Purchase #5 $187.77   8.168%   $203.1071   $203.11   $203.10   $203.10  
  Purchase #6 $70.28   8.675%   $76.3768   $76.38   $76.40   $76.40  
  Purchase #7 $28.44   9.565%   $31.1603   $31.16   $31.15   $31.20  
  7 purchase totals = $671.07       $726.3349   $726.34   $726.30   $726.40