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 $24.99   6.376%   $26.5834   $26.58   $26.60   $26.60  
  Purchase #2 $179.30   5.330%   $188.8567   $188.86   $188.85   $188.90  
  Purchase #3 $82.47   4.160%   $85.9008   $85.90   $85.90   $85.90  
  Purchase #4 $233.85   4.486%   $244.3405   $244.34   $244.35   $244.30  
  Purchase #5 $148.53   3.865%   $154.2707   $154.27   $154.25   $154.30  
  Purchase #6 $219.62   11.558%   $245.0037   $245.00   $245.00   $245.00  
  Purchase #7 $28.35   7.556%   $30.4921   $30.49   $30.50   $30.50  
  7 purchase totals = $917.11       $975.4479   $975.44   $975.45   $975.50