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 $223.53   7.206%   $239.6376   $239.64   $239.65   $239.60  
  Purchase #2 $123.99   5.175%   $130.4065   $130.41   $130.40   $130.40  
  Purchase #3 $124.73   9.250%   $136.2675   $136.27   $136.25   $136.30  
  Purchase #4 $218.85   13.666%   $248.758   $248.76   $248.75   $248.80  
  Purchase #5 $26.82   12.543%   $30.184   $30.18   $30.20   $30.20  
  Purchase #6 $219.51   5.517%   $231.6204   $231.62   $231.60   $231.60  
  Purchase #7 $213.76   7.284%   $229.3303   $229.33   $229.35   $229.30  
  7 purchase totals = $1,151.19       $1,246.2043   $1,246.21   $1,246.20   $1,246.20