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 $86.86   4.710%   $90.9511   $90.95   $90.95   $91.00  
  Purchase #2 $104.95   5.621%   $110.8492   $110.85   $110.85   $110.80  
  Purchase #3 $47.30   8.661%   $51.3967   $51.40   $51.40   $51.40  
  Purchase #4 $235.67   5.794%   $249.3247   $249.32   $249.30   $249.30  
  Purchase #5 $186.60   12.611%   $210.1321   $210.13   $210.15   $210.10  
  Purchase #6 $216.25   3.761%   $224.3832   $224.38   $224.40   $224.40  
  Purchase #7 $96.56   8.179%   $104.4576   $104.46   $104.45   $104.50  
  7 purchase totals = $974.19       $1,041.4946   $1,041.49   $1,041.50   $1,041.50