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 $24.29   7.867%   $26.2009   $26.20   $26.20   $26.20  
  Purchase #2 $50.39   6.802%   $53.8175   $53.82   $53.80   $53.80  
  Purchase #3 $154.69   9.565%   $169.4861   $169.49   $169.50   $169.50  
  Purchase #4 $65.51   7.619%   $70.5012   $70.50   $70.50   $70.50  
  Purchase #5 $144.94   11.426%   $161.5008   $161.50   $161.50   $161.50  
  Purchase #6 $194.78   8.227%   $210.8046   $210.80   $210.80   $210.80  
  Purchase #7 $162.33   13.186%   $183.7348   $183.73   $183.75   $183.70  
  7 purchase totals = $796.93       $876.0459   $876.04   $876.05   $876.00