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 $73.27   8.620%   $79.5859   $79.59   $79.60   $79.60  
  Purchase #2 $248.75   5.632%   $262.7596   $262.76   $262.75   $262.80  
  Purchase #3 $226.39   4.141%   $235.7648   $235.76   $235.75   $235.80  
  Purchase #4 $71.34   3.586%   $73.8983   $73.90   $73.90   $73.90  
  Purchase #5 $223.39   9.455%   $244.5115   $244.51   $244.50   $244.50  
  Purchase #6 $161.67   8.318%   $175.1177   $175.12   $175.10   $175.10  
  Purchase #7 $177.74   6.387%   $189.0923   $189.09   $189.10   $189.10  
  7 purchase totals = $1,182.55       $1,260.7301   $1,260.73   $1,260.70   $1,260.80