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 $236.44   10.529%   $261.3348   $261.33   $261.35   $261.30  
  Purchase #2 $66.32   7.389%   $71.2204   $71.22   $71.20   $71.20  
  Purchase #3 $63.58   5.786%   $67.2587   $67.26   $67.25   $67.30  
  Purchase #4 $32.84   6.731%   $35.0505   $35.05   $35.05   $35.10  
  Purchase #5 $6.28   10.672%   $6.9502   $6.95   $6.95   $7.00  
  Purchase #6 $236.98   4.313%   $247.2009   $247.20   $247.20   $247.20  
  Purchase #7 $226.59   8.539%   $245.9385   $245.94   $245.95   $245.90  
  7 purchase totals = $869.03       $934.9540   $934.95   $934.95   $935.00