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 $226.98   11.449%   $252.9669   $252.97   $252.95   $253.00  
  Purchase #2 $228.87   7.650%   $246.3786   $246.38   $246.40   $246.40  
  Purchase #3 $210.43   5.619%   $222.2541   $222.25   $222.25   $222.30  
  Purchase #4 $72.82   5.172%   $76.5863   $76.59   $76.60   $76.60  
  Purchase #5 $29.61   8.523%   $32.1337   $32.13   $32.15   $32.10  
  Purchase #6 $212.85   11.633%   $237.6108   $237.61   $237.60   $237.60  
  Purchase #7 $244.50   4.685%   $255.9548   $255.95   $255.95   $256.00  
  7 purchase totals = $1,226.06       $1,323.8852   $1,323.88   $1,323.90   $1,324.00