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 $154.95   10.856%   $171.7714   $171.77   $171.75   $171.80  
  Purchase #2 $224.48   11.563%   $250.4366   $250.44   $250.45   $250.40  
  Purchase #3 $119.63   4.823%   $125.3998   $125.40   $125.40   $125.40  
  Purchase #4 $143.94   10.843%   $159.5474   $159.55   $159.55   $159.50  
  Purchase #5 $57.90   6.314%   $61.5558   $61.56   $61.55   $61.60  
  Purchase #6 $209.53   9.762%   $229.9843   $229.98   $230.00   $230.00  
  Purchase #7 $213.49   4.316%   $222.7042   $222.70   $222.70   $222.70  
  7 purchase totals = $1,123.92       $1,221.3995   $1,221.40   $1,221.40   $1,221.40