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 $201.57   12.740%   $227.25   $227.25   $227.25   $227.30  
  Purchase #2 $150.57   3.808%   $156.3037   $156.30   $156.30   $156.30  
  Purchase #3 $81.92   3.697%   $84.9486   $84.95   $84.95   $84.90  
  Purchase #4 $24.85   5.462%   $26.2073   $26.21   $26.20   $26.20  
  Purchase #5 $122.76   13.772%   $139.6665   $139.67   $139.65   $139.70  
  Purchase #6 $107.41   10.666%   $118.8664   $118.87   $118.85   $118.90  
  Purchase #7 $144.63   3.157%   $149.196   $149.20   $149.20   $149.20  
  7 purchase totals = $833.71       $902.4385   $902.45   $902.40   $902.50