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 $219.55   10.367%   $242.3107   $242.31   $242.30   $242.30  
  Purchase #2 $18.37   12.820%   $20.725   $20.73   $20.75   $20.70  
  Purchase #3 $69.63   11.597%   $77.705   $77.71   $77.70   $77.70  
  Purchase #4 $118.59   5.374%   $124.963   $124.96   $124.95   $125.00  
  Purchase #5 $90.41   8.467%   $98.065   $98.07   $98.05   $98.10  
  Purchase #6 $226.55   5.198%   $238.3261   $238.33   $238.35   $238.30  
  Purchase #7 $21.44   8.673%   $23.2995   $23.30   $23.30   $23.30  
  7 purchase totals = $764.54       $825.3943   $825.41   $825.40   $825.40