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	$153.27	12.453%	$172.3567	$172.36	$172.35	$172.40
Purchase #2	$180.50	8.364%	$195.597	$195.60	$195.60	$195.60
Purchase #3	$137.49	10.133%	$151.4219	$151.42	$151.40	$151.40
Purchase #4	$53.59	10.860%	$59.4099	$59.41	$59.40	$59.40
Purchase #5	$70.86	10.103%	$78.019	$78.02	$78.00	$78.00
Purchase #6	$30.77	7.577%	$33.1014	$33.10	$33.10	$33.10
Purchase #7	$87.85	10.267%	$96.8696	$96.87	$96.85	$96.90
7 purchase totals =	$714.33		$786.7755	$786.78	$786.70	$786.80