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 $101.46   12.699%   $114.3444   $114.34   $114.35   $114.30  
  Purchase #2 $25.43   5.202%   $26.7529   $26.75   $26.75   $26.80  
  Purchase #3 $199.76   6.497%   $212.7384   $212.74   $212.75   $212.70  
  Purchase #4 $242.63   4.666%   $253.9511   $253.95   $253.95   $254.00  
  Purchase #5 $102.43   7.151%   $109.7548   $109.75   $109.75   $109.80  
  Purchase #6 $188.38   8.109%   $203.6557   $203.66   $203.65   $203.70  
  Purchase #7 $88.30   11.610%   $98.5516   $98.55   $98.55   $98.60  
  7 purchase totals = $948.39       $1,019.7489   $1,019.74   $1,019.75   $1,019.90