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 $108.28   11.210%   $120.4182   $120.42   $120.40   $120.40  
  Purchase #2 $173.43   10.103%   $190.9516   $190.95   $190.95   $191.00  
  Purchase #3 $131.79   8.131%   $142.5058   $142.51   $142.50   $142.50  
  Purchase #4 $201.49   11.177%   $224.0105   $224.01   $224.00   $224.00  
  Purchase #5 $241.54   8.156%   $261.24   $261.24   $261.25   $261.20  
  Purchase #6 $67.43   6.553%   $71.8487   $71.85   $71.85   $71.80  
  Purchase #7 $104.78   3.423%   $108.3666   $108.37   $108.35   $108.40  
  7 purchase totals = $1,028.74       $1,119.3414   $1,119.35   $1,119.30   $1,119.30