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 $162.96   8.244%   $176.3944   $176.39   $176.40   $176.40  
  Purchase #2 $196.49   10.540%   $217.2   $217.20   $217.20   $217.20  
  Purchase #3 $55.89   4.190%   $58.2318   $58.23   $58.25   $58.20  
  Purchase #4 $51.68   3.118%   $53.2914   $53.29   $53.30   $53.30  
  Purchase #5 $161.55   13.289%   $183.0184   $183.02   $183.00   $183.00  
  Purchase #6 $245.54   5.545%   $259.1552   $259.16   $259.15   $259.20  
  Purchase #7 $18.63   8.695%   $20.2499   $20.25   $20.25   $20.20  
  7 purchase totals = $892.74       $967.5411   $967.54   $967.55   $967.50