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 $114.81   8.349%   $124.3955   $124.40   $124.40   $124.40  
  Purchase #2 $178.44   9.549%   $195.4792   $195.48   $195.50   $195.50  
  Purchase #3 $60.77   8.313%   $65.8218   $65.82   $65.80   $65.80  
  Purchase #4 $173.46   6.869%   $185.375   $185.38   $185.40   $185.40  
  Purchase #5 $49.81   11.677%   $55.6263   $55.63   $55.65   $55.60  
  Purchase #6 $103.98   13.291%   $117.8   $117.80   $117.80   $117.80  
  Purchase #7 $43.76   9.764%   $48.0327   $48.03   $48.05   $48.00  
  7 purchase totals = $725.03       $792.5305   $792.54   $792.60   $792.50