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 $182.27   12.247%   $204.5926   $204.59   $204.60   $204.60  
  Purchase #2 $224.77   4.640%   $235.1993   $235.20   $235.20   $235.20  
  Purchase #3 $178.94   6.203%   $190.0396   $190.04   $190.05   $190.00  
  Purchase #4 $244.35   9.674%   $267.9884   $267.99   $268.00   $268.00  
  Purchase #5 $192.27   13.260%   $217.765   $217.77   $217.75   $217.80  
  Purchase #6 $48.84   12.366%   $54.8796   $54.88   $54.90   $54.90  
  Purchase #7 $178.49   4.128%   $185.8581   $185.86   $185.85   $185.90  
  7 purchase totals = $1,249.93       $1,356.3226   $1,356.33   $1,356.35   $1,356.40