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 $77.96   5.209%   $82.0209   $82.02   $82.00   $82.00  
  Purchase #2 $112.64   11.824%   $125.9586   $125.96   $125.95   $126.00  
  Purchase #3 $152.28   13.772%   $173.252   $173.25   $173.25   $173.30  
  Purchase #4 $56.62   10.462%   $62.5436   $62.54   $62.55   $62.50  
  Purchase #5 $204.73   3.151%   $211.181   $211.18   $211.20   $211.20  
  Purchase #6 $234.64   6.301%   $249.4247   $249.42   $249.40   $249.40  
  Purchase #7 $10.43   4.459%   $10.8951   $10.90   $10.90   $10.90  
  7 purchase totals = $849.30       $915.2759   $915.27   $915.25   $915.30