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 $119.95   5.299%   $126.3062   $126.31   $126.30   $126.30  
  Purchase #2 $162.62   8.425%   $176.3207   $176.32   $176.30   $176.30  
  Purchase #3 $86.92   5.469%   $91.6737   $91.67   $91.65   $91.70  
  Purchase #4 $107.27   9.163%   $117.0992   $117.10   $117.10   $117.10  
  Purchase #5 $166.58   4.606%   $174.2527   $174.25   $174.25   $174.30  
  Purchase #6 $250.27   3.726%   $259.5951   $259.60   $259.60   $259.60  
  Purchase #7 $38.73   9.656%   $42.4698   $42.47   $42.45   $42.50  
  7 purchase totals = $932.34       $987.7174   $987.72   $987.65   $987.80