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	$133.48	13.509%	$151.5118	$151.51	$151.50	$151.50
Purchase #2	$53.45	9.103%	$58.3156	$58.32	$58.30	$58.30
Purchase #3	$210.42	10.840%	$233.2295	$233.23	$233.25	$233.20
Purchase #4	$50.56	12.469%	$56.8643	$56.86	$56.85	$56.90
Purchase #5	$58.58	11.569%	$65.3571	$65.36	$65.35	$65.40
Purchase #6	$76.60	7.221%	$82.1313	$82.13	$82.15	$82.10
Purchase #7	$114.77	12.343%	$128.9361	$128.94	$128.95	$128.90
7 purchase totals =	$697.86		$776.3457	$776.35	$776.35	$776.30