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	$62.81	11.730%	$70.1776	$70.18	$70.20	$70.20
Purchase #2	$231.99	4.597%	$242.6546	$242.65	$242.65	$242.70
Purchase #3	$102.45	6.513%	$109.1226	$109.12	$109.10	$109.10
Purchase #4	$35.78	3.244%	$36.9407	$36.94	$36.95	$36.90
Purchase #5	$33.68	12.404%	$37.8577	$37.86	$37.85	$37.90
Purchase #6	$164.72	4.836%	$172.6859	$172.69	$172.70	$172.70
Purchase #7	$214.80	12.116%	$240.8252	$240.83	$240.85	$240.80
7 purchase totals =	$846.23		$910.2643	$910.27	$910.30	$910.30