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 $93.27   8.792%   $101.4703   $101.47   $101.45   $101.50  
  Purchase #2 $88.64   3.559%   $91.7947   $91.79   $91.80   $91.80  
  Purchase #3 $24.28   9.545%   $26.5975   $26.60   $26.60   $26.60  
  Purchase #4 $46.61   10.314%   $51.4174   $51.42   $51.40   $51.40  
  Purchase #5 $104.83   5.671%   $110.7749   $110.77   $110.75   $110.80  
  Purchase #6 $89.76   9.135%   $97.9596   $97.96   $97.95   $98.00  
  Purchase #7 $246.84   5.352%   $260.0509   $260.05   $260.05   $260.10  
  7 purchase totals = $694.23       $740.0653   $740.06   $740.00   $740.20