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 $16.94   7.645%   $18.2351   $18.24   $18.25   $18.20  
  Purchase #2 $5.86   7.704%   $6.3115   $6.31   $6.30   $6.30  
  Purchase #3 $87.83   4.579%   $91.8517   $91.85   $91.85   $91.90  
  Purchase #4 $10.74   5.426%   $11.3228   $11.32   $11.30   $11.30  
  Purchase #5 $49.40   12.291%   $55.4718   $55.47   $55.45   $55.50  
  Purchase #6 $78.75   5.406%   $83.0072   $83.01   $83.00   $83.00  
  Purchase #7 $244.40   13.795%   $278.115   $278.12   $278.10   $278.10  
  7 purchase totals = $493.92       $544.3151   $544.32   $544.25   $544.30