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 $200.87   6.569%   $214.0652   $214.07   $214.05   $214.10  
  Purchase #2 $31.57   4.221%   $32.9026   $32.90   $32.90   $32.90  
  Purchase #3 $228.31   7.158%   $244.6524   $244.65   $244.65   $244.70  
  Purchase #4 $49.41   8.334%   $53.5278   $53.53   $53.55   $53.50  
  Purchase #5 $244.73   6.201%   $259.9057   $259.91   $259.90   $259.90  
  Purchase #6 $5.89   6.312%   $6.2618   $6.26   $6.25   $6.30  
  Purchase #7 $202.31   7.337%   $217.1535   $217.15   $217.15   $217.20  
  7 purchase totals = $963.09       $1,028.4690   $1,028.47   $1,028.45   $1,028.60