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 $68.97   8.689%   $74.9628   $74.96   $74.95   $75.00  
  Purchase #2 $104.34   11.342%   $116.1742   $116.17   $116.15   $116.20  
  Purchase #3 $60.59   6.195%   $64.3436   $64.34   $64.35   $64.30  
  Purchase #4 $213.29   3.319%   $220.3691   $220.37   $220.35   $220.40  
  Purchase #5 $56.30   13.237%   $63.7524   $63.75   $63.75   $63.80  
  Purchase #6 $227.90   9.644%   $249.8787   $249.88   $249.90   $249.90  
  Purchase #7 $124.62   11.510%   $138.9638   $138.96   $138.95   $139.00  
  7 purchase totals = $856.01       $928.4446   $928.43   $928.40   $928.60