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 $177.27   3.644%   $183.7297   $183.73   $183.75   $183.70  
  Purchase #2 $176.43   12.859%   $199.1171   $199.12   $199.10   $199.10  
  Purchase #3 $30.92   10.117%   $34.0482   $34.05   $34.05   $34.00  
  Purchase #4 $244.49   12.794%   $275.7701   $275.77   $275.75   $275.80  
  Purchase #5 $90.92   3.669%   $94.2559   $94.26   $94.25   $94.30  
  Purchase #6 $202.95   10.863%   $224.9965   $225.00   $225.00   $225.00  
  Purchase #7 $153.68   12.796%   $173.3449   $173.34   $173.35   $173.30  
  7 purchase totals = $1,076.66       $1,185.2624   $1,185.27   $1,185.25   $1,185.20