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 $243.87   7.177%   $261.3725   $261.37   $261.35   $261.40  
  Purchase #2 $158.90   11.695%   $177.4834   $177.48   $177.50   $177.50  
  Purchase #3 $246.73   6.761%   $263.4114   $263.41   $263.40   $263.40  
  Purchase #4 $62.32   5.341%   $65.6485   $65.65   $65.65   $65.60  
  Purchase #5 $32.46   4.752%   $34.0025   $34.00   $34.00   $34.00  
  Purchase #6 $182.78   11.185%   $203.2239   $203.22   $203.20   $203.20  
  Purchase #7 $20.92   12.246%   $23.4819   $23.48   $23.50   $23.50  
  7 purchase totals = $947.98       $1,028.6241   $1,028.61   $1,028.60   $1,028.60