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 $117.33   6.319%   $124.7441   $124.74   $124.75   $124.70  
  Purchase #2 $141.65   10.414%   $156.4014   $156.40   $156.40   $156.40  
  Purchase #3 $22.26   5.313%   $23.4427   $23.44   $23.45   $23.40  
  Purchase #4 $190.28   7.211%   $204.0011   $204.00   $204.00   $204.00  
  Purchase #5 $46.77   12.523%   $52.627   $52.63   $52.65   $52.60  
  Purchase #6 $24.80   4.653%   $25.9539   $25.95   $25.95   $26.00  
  Purchase #7 $194.54   6.399%   $206.9886   $206.99   $207.00   $207.00  
  7 purchase totals = $737.63       $794.1588   $794.15   $794.20   $794.10