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 $119.37   10.744%   $132.1951   $132.20   $132.20   $132.20  
  Purchase #2 $231.88   7.741%   $249.8298   $249.83   $249.85   $249.80  
  Purchase #3 $70.90   11.567%   $79.101   $79.10   $79.10   $79.10  
  Purchase #4 $234.82   5.236%   $247.1152   $247.12   $247.10   $247.10  
  Purchase #5 $73.50   6.399%   $78.2033   $78.20   $78.20   $78.20  
  Purchase #6 $92.37   13.632%   $104.9619   $104.96   $104.95   $105.00  
  Purchase #7 $59.30   12.800%   $66.8904   $66.89   $66.90   $66.90  
  7 purchase totals = $882.14       $958.2967   $958.30   $958.30   $958.30