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 $19.48   12.658%   $21.9458   $21.95   $21.95   $21.90  
  Purchase #2 $195.71   13.630%   $222.3853   $222.39   $222.40   $222.40  
  Purchase #3 $174.52   12.305%   $195.9947   $195.99   $196.00   $196.00  
  Purchase #4 $77.63   6.187%   $82.433   $82.43   $82.45   $82.40  
  Purchase #5 $102.49   9.437%   $112.162   $112.16   $112.15   $112.20  
  Purchase #6 $68.97   6.134%   $73.2006   $73.20   $73.20   $73.20  
  Purchase #7 $230.66   5.302%   $242.8896   $242.89   $242.90   $242.90  
  7 purchase totals = $869.46       $951.0110   $951.01   $951.05   $951.00