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 $186.95   4.284%   $194.9589   $194.96   $194.95   $195.00  
  Purchase #2 $19.27   12.236%   $21.6279   $21.63   $21.65   $21.60  
  Purchase #3 $111.56   5.449%   $117.6389   $117.64   $117.65   $117.60  
  Purchase #4 $23.94   11.630%   $26.7242   $26.72   $26.70   $26.70  
  Purchase #5 $175.96   8.826%   $191.4902   $191.49   $191.50   $191.50  
  Purchase #6 $125.56   5.181%   $132.0653   $132.07   $132.05   $132.10  
  Purchase #7 $108.38   8.423%   $117.5088   $117.51   $117.50   $117.50  
  7 purchase totals = $751.62       $802.0142   $802.02   $802.00   $802.00