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 $55.60   10.277%   $61.314   $61.31   $61.30   $61.30  
  Purchase #2 $115.63   8.452%   $125.403   $125.40   $125.40   $125.40  
  Purchase #3 $202.82   3.281%   $209.4745   $209.47   $209.45   $209.50  
  Purchase #4 $118.91   9.744%   $130.4966   $130.50   $130.50   $130.50  
  Purchase #5 $59.73   12.806%   $67.379   $67.38   $67.40   $67.40  
  Purchase #6 $185.45   4.761%   $194.2793   $194.28   $194.30   $194.30  
  Purchase #7 $220.95   13.466%   $250.7031   $250.70   $250.70   $250.70  
  7 purchase totals = $959.09       $1,039.0495   $1,039.04   $1,039.05   $1,039.10