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 $217.76   8.386%   $236.0214   $236.02   $236.00   $236.00  
  Purchase #2 $247.84   8.448%   $268.7775   $268.78   $268.80   $268.80  
  Purchase #3 $88.79   4.757%   $93.0137   $93.01   $93.00   $93.00  
  Purchase #4 $122.72   6.341%   $130.5017   $130.50   $130.50   $130.50  
  Purchase #5 $231.51   12.818%   $261.185   $261.19   $261.20   $261.20  
  Purchase #6 $64.41   4.331%   $67.1996   $67.20   $67.20   $67.20  
  Purchase #7 $6.26   7.502%   $6.7296   $6.73   $6.75   $6.70  
  7 purchase totals = $979.29       $1,063.4285   $1,063.43   $1,063.45   $1,063.40