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 $65.69   4.667%   $68.7558   $68.76   $68.75   $68.80  
  Purchase #2 $57.26   8.302%   $62.0137   $62.01   $62.00   $62.00  
  Purchase #3 $66.85   11.752%   $74.7062   $74.71   $74.70   $74.70  
  Purchase #4 $148.40   9.464%   $162.4446   $162.44   $162.45   $162.40  
  Purchase #5 $174.51   4.380%   $182.1535   $182.15   $182.15   $182.20  
  Purchase #6 $115.80   3.321%   $119.6457   $119.65   $119.65   $119.60  
  Purchase #7 $92.56   12.513%   $104.142   $104.14   $104.15   $104.10  
  7 purchase totals = $721.07       $773.8615   $773.86   $773.85   $773.80