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 $61.83   6.673%   $65.9559   $65.96   $65.95   $66.00  
  Purchase #2 $108.82   4.716%   $113.952   $113.95   $113.95   $114.00  
  Purchase #3 $152.31   4.699%   $159.467   $159.47   $159.45   $159.50  
  Purchase #4 $68.91   10.147%   $75.9023   $75.90   $75.90   $75.90  
  Purchase #5 $20.66   12.796%   $23.3037   $23.30   $23.30   $23.30  
  Purchase #6 $107.39   11.129%   $119.3414   $119.34   $119.35   $119.30  
  Purchase #7 $236.71   4.483%   $247.3217   $247.32   $247.30   $247.30  
  7 purchase totals = $756.63       $805.2440   $805.24   $805.20   $805.30