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 $60.73   3.452%   $62.8264   $62.83   $62.85   $62.80  
  Purchase #2 $246.36   9.153%   $268.9093   $268.91   $268.90   $268.90  
  Purchase #3 $132.89   10.133%   $146.3557   $146.36   $146.35   $146.40  
  Purchase #4 $22.47   13.552%   $25.5151   $25.52   $25.50   $25.50  
  Purchase #5 $210.69   12.121%   $236.2277   $236.23   $236.25   $236.20  
  Purchase #6 $48.36   8.541%   $52.4904   $52.49   $52.50   $52.50  
  Purchase #7 $135.39   4.434%   $141.3932   $141.39   $141.40   $141.40  
  7 purchase totals = $856.89       $933.7178   $933.73   $933.75   $933.70