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 $217.44   7.427%   $233.5893   $233.59   $233.60   $233.60  
  Purchase #2 $177.92   8.756%   $193.4987   $193.50   $193.50   $193.50  
  Purchase #3 $194.26   5.115%   $204.1964   $204.20   $204.20   $204.20  
  Purchase #4 $127.83   8.652%   $138.8899   $138.89   $138.90   $138.90  
  Purchase #5 $68.75   12.686%   $77.4716   $77.47   $77.45   $77.50  
  Purchase #6 $157.83   13.793%   $179.5995   $179.60   $179.60   $179.60  
  Purchase #7 $143.59   3.754%   $148.9804   $148.98   $149.00   $149.00  
  7 purchase totals = $1,087.62       $1,176.2258   $1,176.23   $1,176.25   $1,176.30