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 $208.84   5.622%   $220.581   $220.58   $220.60   $220.60  
  Purchase #2 $67.63   5.638%   $71.443   $71.44   $71.45   $71.40  
  Purchase #3 $110.30   7.800%   $118.9034   $118.90   $118.90   $118.90  
  Purchase #4 $125.35   9.565%   $137.3397   $137.34   $137.35   $137.30  
  Purchase #5 $66.44   11.182%   $73.8693   $73.87   $73.85   $73.90  
  Purchase #6 $141.25   8.433%   $153.1616   $153.16   $153.15   $153.20  
  Purchase #7 $17.98   4.533%   $18.795   $18.80   $18.80   $18.80  
  7 purchase totals = $737.79       $794.0930   $794.09   $794.10   $794.10