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 $232.49   9.267%   $254.0348   $254.03   $254.05   $254.00  
  Purchase #2 $210.44   6.584%   $224.2954   $224.30   $224.30   $224.30  
  Purchase #3 $113.69   7.462%   $122.1735   $122.17   $122.15   $122.20  
  Purchase #4 $74.47   5.652%   $78.679   $78.68   $78.70   $78.70  
  Purchase #5 $30.60   7.577%   $32.9186   $32.92   $32.90   $32.90  
  Purchase #6 $131.87   11.683%   $147.2764   $147.28   $147.30   $147.30  
  Purchase #7 $192.67   12.744%   $217.2239   $217.22   $217.20   $217.20  
  7 purchase totals = $986.23       $1,076.6016   $1,076.60   $1,076.60   $1,076.60