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 $241.57   8.170%   $261.3063   $261.31   $261.30   $261.30  
  Purchase #2 $235.77   9.491%   $258.1469   $258.15   $258.15   $258.10  
  Purchase #3 $99.36   5.371%   $104.6966   $104.70   $104.70   $104.70  
  Purchase #4 $188.30   8.554%   $204.4072   $204.41   $204.40   $204.40  
  Purchase #5 $189.37   5.309%   $199.4237   $199.42   $199.40   $199.40  
  Purchase #6 $214.99   4.324%   $224.2862   $224.29   $224.30   $224.30  
  Purchase #7 $232.99   3.150%   $240.3292   $240.33   $240.35   $240.30  
  7 purchase totals = $1,402.35       $1,492.5961   $1,492.61   $1,492.60   $1,492.50