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 $93.55   8.110%   $101.1369   $101.14   $101.15   $101.10  
  Purchase #2 $56.82   5.419%   $59.8991   $59.90   $59.90   $59.90  
  Purchase #3 $48.83   12.134%   $54.755   $54.76   $54.75   $54.80  
  Purchase #4 $29.26   13.507%   $33.2121   $33.21   $33.20   $33.20  
  Purchase #5 $232.39   12.440%   $261.2993   $261.30   $261.30   $261.30  
  Purchase #6 $44.62   13.133%   $50.4799   $50.48   $50.50   $50.50  
  Purchase #7 $191.51   3.592%   $198.389   $198.39   $198.40   $198.40  
  7 purchase totals = $696.98       $759.1713   $759.18   $759.20   $759.20