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 $87.84   10.793%   $97.3206   $97.32   $97.30   $97.30  
  Purchase #2 $206.29   8.494%   $223.8123   $223.81   $223.80   $223.80  
  Purchase #3 $128.48   10.413%   $141.8586   $141.86   $141.85   $141.90  
  Purchase #4 $139.25   10.770%   $154.2472   $154.25   $154.25   $154.20  
  Purchase #5 $190.54   9.622%   $208.8738   $208.87   $208.85   $208.90  
  Purchase #6 $112.99   5.622%   $119.3423   $119.34   $119.35   $119.30  
  Purchase #7 $13.43   4.135%   $13.9853   $13.99   $14.00   $14.00  
  7 purchase totals = $878.82       $959.4401   $959.44   $959.40   $959.40