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 $244.77   4.590%   $256.0049   $256.00   $256.00   $256.00  
  Purchase #2 $210.54   7.597%   $226.5347   $226.53   $226.55   $226.50  
  Purchase #3 $244.32   6.667%   $260.6088   $260.61   $260.60   $260.60  
  Purchase #4 $189.87   9.665%   $208.2209   $208.22   $208.20   $208.20  
  Purchase #5 $175.38   11.421%   $195.4101   $195.41   $195.40   $195.40  
  Purchase #6 $104.97   4.301%   $109.4848   $109.48   $109.50   $109.50  
  Purchase #7 $227.30   5.257%   $239.2492   $239.25   $239.25   $239.20  
  7 purchase totals = $1,397.15       $1,495.5134   $1,495.50   $1,495.50   $1,495.40