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 $69.62   8.713%   $75.686   $75.69   $75.70   $75.70  
  Purchase #2 $97.26   12.260%   $109.1841   $109.18   $109.20   $109.20  
  Purchase #3 $23.63   13.786%   $26.8876   $26.89   $26.90   $26.90  
  Purchase #4 $176.28   11.170%   $195.9705   $195.97   $195.95   $196.00  
  Purchase #5 $99.49   5.766%   $105.2266   $105.23   $105.25   $105.20  
  Purchase #6 $158.89   10.688%   $175.8722   $175.87   $175.85   $175.90  
  Purchase #7 $54.89   8.240%   $59.4129   $59.41   $59.40   $59.40  
  7 purchase totals = $680.06       $748.2399   $748.24   $748.25   $748.30