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 $224.86   12.847%   $253.7478   $253.75   $253.75   $253.70  
  Purchase #2 $204.68   12.662%   $230.5966   $230.60   $230.60   $230.60  
  Purchase #3 $34.72   7.335%   $37.2667   $37.27   $37.25   $37.30  
  Purchase #4 $19.89   5.252%   $20.9346   $20.93   $20.95   $20.90  
  Purchase #5 $119.25   9.546%   $130.6336   $130.63   $130.65   $130.60  
  Purchase #6 $114.70   11.786%   $128.2185   $128.22   $128.20   $128.20  
  Purchase #7 $163.78   9.423%   $179.213   $179.21   $179.20   $179.20  
  7 purchase totals = $881.88       $980.6108   $980.61   $980.60   $980.50