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 $168.55   4.406%   $175.9763   $175.98   $176.00   $176.00  
  Purchase #2 $13.94   7.238%   $14.949   $14.95   $14.95   $14.90  
  Purchase #3 $245.65   6.413%   $261.4035   $261.40   $261.40   $261.40  
  Purchase #4 $151.72   8.199%   $164.1595   $164.16   $164.15   $164.20  
  Purchase #5 $63.79   4.735%   $66.8105   $66.81   $66.80   $66.80  
  Purchase #6 $43.50   11.590%   $48.5417   $48.54   $48.55   $48.50  
  Purchase #7 $70.57   10.788%   $78.1831   $78.18   $78.20   $78.20  
  7 purchase totals = $757.72       $810.0236   $810.02   $810.05   $810.00