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 $24.99   5.412%   $26.3425   $26.34   $26.35   $26.30  
  Purchase #2 $182.99   12.548%   $205.9516   $205.95   $205.95   $206.00  
  Purchase #3 $243.29   10.775%   $269.5045   $269.50   $269.50   $269.50  
  Purchase #4 $235.99   3.434%   $244.0939   $244.09   $244.10   $244.10  
  Purchase #5 $143.97   3.428%   $148.9053   $148.91   $148.90   $148.90  
  Purchase #6 $194.39   7.241%   $208.4658   $208.47   $208.45   $208.50  
  Purchase #7 $72.49   7.844%   $78.1761   $78.18   $78.20   $78.20  
  7 purchase totals = $1,098.11       $1,181.4397   $1,181.44   $1,181.45   $1,181.50