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 $227.29   9.533%   $248.9576   $248.96   $248.95   $249.00  
  Purchase #2 $162.51   12.601%   $182.9879   $182.99   $183.00   $183.00  
  Purchase #3 $228.74   6.737%   $244.1502   $244.15   $244.15   $244.20  
  Purchase #4 $15.59   10.781%   $17.2708   $17.27   $17.25   $17.30  
  Purchase #5 $198.54   9.784%   $217.9652   $217.97   $217.95   $218.00  
  Purchase #6 $51.96   4.200%   $54.1423   $54.14   $54.15   $54.10  
  Purchase #7 $243.83   13.153%   $275.901   $275.90   $275.90   $275.90  
  7 purchase totals = $1,128.46       $1,241.3750   $1,241.38   $1,241.35   $1,241.50