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 $54.97   10.197%   $60.5753   $60.58   $60.60   $60.60  
  Purchase #2 $170.69   6.706%   $182.1365   $182.14   $182.15   $182.10  
  Purchase #3 $11.43   9.853%   $12.5562   $12.56   $12.55   $12.60  
  Purchase #4 $178.79   5.136%   $187.9727   $187.97   $187.95   $188.00  
  Purchase #5 $185.40   9.238%   $202.5273   $202.53   $202.55   $202.50  
  Purchase #6 $61.53   8.441%   $66.7237   $66.72   $66.70   $66.70  
  Purchase #7 $210.49   9.527%   $230.5434   $230.54   $230.55   $230.50  
  7 purchase totals = $873.30       $943.0351   $943.04   $943.05   $943.00