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 $218.68   12.168%   $245.289   $245.29   $245.30   $245.30  
  Purchase #2 $15.80   13.161%   $17.8794   $17.88   $17.90   $17.90  
  Purchase #3 $73.61   6.855%   $78.656   $78.66   $78.65   $78.70  
  Purchase #4 $133.33   4.583%   $139.4405   $139.44   $139.45   $139.40  
  Purchase #5 $178.28   9.180%   $194.6461   $194.65   $194.65   $194.60  
  Purchase #6 $93.93   7.691%   $101.1542   $101.15   $101.15   $101.20  
  Purchase #7 $76.63   6.810%   $81.8485   $81.85   $81.85   $81.80  
  7 purchase totals = $790.26       $858.9137   $858.92   $858.95   $858.90