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 $89.54   13.308%   $101.456   $101.46   $101.45   $101.50  
  Purchase #2 $54.51   7.529%   $58.6141   $58.61   $58.60   $58.60  
  Purchase #3 $152.32   7.610%   $163.9116   $163.91   $163.90   $163.90  
  Purchase #4 $224.69   11.131%   $249.7002   $249.70   $249.70   $249.70  
  Purchase #5 $46.50   10.192%   $51.2393   $51.24   $51.25   $51.20  
  Purchase #6 $54.43   12.429%   $61.1951   $61.20   $61.20   $61.20  
  Purchase #7 $250.62   9.244%   $273.7873   $273.79   $273.80   $273.80  
  7 purchase totals = $872.61       $959.9036   $959.91   $959.90   $959.90