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 $59.88   4.277%   $62.4411   $62.44   $62.45   $62.40  
  Purchase #2 $197.87   3.412%   $204.6213   $204.62   $204.60   $204.60  
  Purchase #3 $180.47   10.543%   $199.497   $199.50   $199.50   $199.50  
  Purchase #4 $124.85   12.576%   $140.5511   $140.55   $140.55   $140.60  
  Purchase #5 $86.90   8.302%   $94.1144   $94.11   $94.10   $94.10  
  Purchase #6 $88.27   12.161%   $99.0045   $99.00   $99.00   $99.00  
  Purchase #7 $101.47   9.867%   $111.482   $111.48   $111.50   $111.50  
  7 purchase totals = $839.71       $911.7114   $911.70   $911.70   $911.70