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 $249.33   7.226%   $267.3466   $267.35   $267.35   $267.30  
  Purchase #2 $60.74   3.169%   $62.6649   $62.66   $62.65   $62.70  
  Purchase #3 $19.58   10.339%   $21.6044   $21.60   $21.60   $21.60  
  Purchase #4 $126.25   5.153%   $132.7557   $132.76   $132.75   $132.80  
  Purchase #5 $183.45   13.789%   $208.7459   $208.75   $208.75   $208.70  
  Purchase #6 $208.56   10.221%   $229.8769   $229.88   $229.90   $229.90  
  Purchase #7 $136.31   7.417%   $146.4201   $146.42   $146.40   $146.40  
  7 purchase totals = $984.22       $1,069.4145   $1,069.42   $1,069.40   $1,069.40