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 $125.47   13.413%   $142.2993   $142.30   $142.30   $142.30  
  Purchase #2 $210.63   8.176%   $227.8511   $227.85   $227.85   $227.90  
  Purchase #3 $169.25   4.504%   $176.873   $176.87   $176.85   $176.90  
  Purchase #4 $143.74   9.149%   $156.8908   $156.89   $156.90   $156.90  
  Purchase #5 $126.84   12.686%   $142.9309   $142.93   $142.95   $142.90  
  Purchase #6 $240.55   10.811%   $266.5559   $266.56   $266.55   $266.60  
  Purchase #7 $113.75   11.597%   $126.9416   $126.94   $126.95   $126.90  
  7 purchase totals = $1,130.23       $1,240.3426   $1,240.34   $1,240.35   $1,240.40