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 $124.47   8.872%   $135.513   $135.51   $135.50   $135.50  
  Purchase #2 $206.43   10.169%   $227.4219   $227.42   $227.40   $227.40  
  Purchase #3 $164.34   11.262%   $182.848   $182.85   $182.85   $182.80  
  Purchase #4 $107.47   7.569%   $115.6044   $115.60   $115.60   $115.60  
  Purchase #5 $119.51   4.412%   $124.7828   $124.78   $124.80   $124.80  
  Purchase #6 $104.67   5.444%   $110.3682   $110.37   $110.35   $110.40  
  Purchase #7 $124.97   11.632%   $139.5065   $139.51   $139.50   $139.50  
  7 purchase totals = $951.86       $1,036.0448   $1,036.04   $1,036.00   $1,036.00