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 $22.91   13.548%   $26.0138   $26.01   $26.00   $26.00  
  Purchase #2 $215.27   11.758%   $240.5814   $240.58   $240.60   $240.60  
  Purchase #3 $17.77   6.333%   $18.8954   $18.90   $18.90   $18.90  
  Purchase #4 $228.42   5.323%   $240.5788   $240.58   $240.60   $240.60  
  Purchase #5 $73.79   3.659%   $76.49   $76.49   $76.50   $76.50  
  Purchase #6 $85.68   5.162%   $90.1028   $90.10   $90.10   $90.10  
  Purchase #7 $204.81   11.137%   $227.6197   $227.62   $227.60   $227.60  
  7 purchase totals = $848.65       $920.2819   $920.28   $920.30   $920.30