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 $53.71   8.810%   $58.4419   $58.44   $58.45   $58.40  
  Purchase #2 $134.77   5.493%   $142.1729   $142.17   $142.15   $142.20  
  Purchase #3 $178.38   9.561%   $195.4349   $195.43   $195.45   $195.40  
  Purchase #4 $105.37   13.706%   $119.812   $119.81   $119.80   $119.80  
  Purchase #5 $185.78   11.186%   $206.5614   $206.56   $206.55   $206.60  
  Purchase #6 $100.43   4.549%   $104.9986   $105.00   $105.00   $105.00  
  Purchase #7 $123.79   6.834%   $132.2498   $132.25   $132.25   $132.20  
  7 purchase totals = $882.23       $959.6715   $959.66   $959.65   $959.60