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 $118.91   6.299%   $126.4001   $126.40   $126.40   $126.40  
  Purchase #2 $110.44   5.216%   $116.2006   $116.20   $116.20   $116.20  
  Purchase #3 $126.38   13.844%   $143.876   $143.88   $143.90   $143.90  
  Purchase #4 $13.84   13.793%   $15.749   $15.75   $15.75   $15.70  
  Purchase #5 $98.96   10.797%   $109.6447   $109.64   $109.65   $109.60  
  Purchase #6 $169.51   8.347%   $183.659   $183.66   $183.65   $183.70  
  Purchase #7 $65.66   13.551%   $74.5576   $74.56   $74.55   $74.60  
  7 purchase totals = $703.70       $770.0870   $770.09   $770.10   $770.10