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 $59.40   12.726%   $66.9592   $66.96   $66.95   $67.00  
  Purchase #2 $66.56   4.409%   $69.4946   $69.49   $69.50   $69.50  
  Purchase #3 $60.33   6.355%   $64.164   $64.16   $64.15   $64.20  
  Purchase #4 $201.51   5.853%   $213.3044   $213.30   $213.30   $213.30  
  Purchase #5 $242.81   5.463%   $256.0747   $256.07   $256.05   $256.10  
  Purchase #6 $39.54   4.325%   $41.2501   $41.25   $41.25   $41.30  
  Purchase #7 $45.37   3.844%   $47.114   $47.11   $47.10   $47.10  
  7 purchase totals = $715.52       $758.3610   $758.34   $758.30   $758.50