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 $23.75   12.593%   $26.7408   $26.74   $26.75   $26.70  
  Purchase #2 $225.78   8.360%   $244.6552   $244.66   $244.65   $244.70  
  Purchase #3 $9.38   11.252%   $10.4354   $10.44   $10.45   $10.40  
  Purchase #4 $157.84   6.856%   $168.6615   $168.66   $168.65   $168.70  
  Purchase #5 $18.84   7.223%   $20.2008   $20.20   $20.20   $20.20  
  Purchase #6 $188.80   8.600%   $205.0368   $205.04   $205.05   $205.00  
  Purchase #7 $69.61   9.597%   $76.2905   $76.29   $76.30   $76.30  
  7 purchase totals = $694.00       $752.0210   $752.03   $752.05   $752.00