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 $24.43   7.416%   $26.2417   $26.24   $26.25   $26.20  
  Purchase #2 $44.34   12.251%   $49.7721   $49.77   $49.75   $49.80  
  Purchase #3 $207.35   3.290%   $214.1718   $214.17   $214.15   $214.20  
  Purchase #4 $56.47   11.330%   $62.8681   $62.87   $62.85   $62.90  
  Purchase #5 $212.34   3.738%   $220.2773   $220.28   $220.30   $220.30  
  Purchase #6 $157.25   3.857%   $163.3151   $163.32   $163.30   $163.30  
  Purchase #7 $20.63   3.341%   $21.3192   $21.32   $21.30   $21.30  
  7 purchase totals = $722.81       $757.9653   $757.97   $757.90   $758.00