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 $221.97   5.748%   $234.7288   $234.73   $234.75   $234.70  
  Purchase #2 $217.89   13.166%   $246.5774   $246.58   $246.60   $246.60  
  Purchase #3 $21.47   4.725%   $22.4845   $22.48   $22.50   $22.50  
  Purchase #4 $51.53   6.871%   $55.0706   $55.07   $55.05   $55.10  
  Purchase #5 $55.78   12.655%   $62.839   $62.84   $62.85   $62.80  
  Purchase #6 $195.95   7.657%   $210.9539   $210.95   $210.95   $211.00  
  Purchase #7 $169.76   5.144%   $178.4925   $178.49   $178.50   $178.50  
  7 purchase totals = $934.35       $1,011.1467   $1,011.14   $1,011.20   $1,011.20