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 $74.53   6.342%   $79.2567   $79.26   $79.25   $79.30  
  Purchase #2 $210.42   13.866%   $239.5968   $239.60   $239.60   $239.60  
  Purchase #3 $11.27   8.464%   $12.2239   $12.22   $12.20   $12.20  
  Purchase #4 $216.40   10.391%   $238.8861   $238.89   $238.90   $238.90  
  Purchase #5 $205.51   4.777%   $215.3272   $215.33   $215.35   $215.30  
  Purchase #6 $78.75   6.536%   $83.8971   $83.90   $83.90   $83.90  
  Purchase #7 $139.67   10.806%   $154.7627   $154.76   $154.75   $154.80  
  7 purchase totals = $936.55       $1,023.9505   $1,023.96   $1,023.95   $1,024.00