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	$57.59	12.103%	$64.5601	$64.56	$64.55	$64.60
Purchase #2	$57.88	5.836%	$61.2579	$61.26	$61.25	$61.30
Purchase #3	$162.42	6.818%	$173.4938	$173.49	$173.50	$173.50
Purchase #4	$105.97	11.485%	$118.1407	$118.14	$118.15	$118.10
Purchase #5	$178.90	8.311%	$193.7684	$193.77	$193.75	$193.80
Purchase #6	$55.98	6.210%	$59.4564	$59.46	$59.45	$59.50
Purchase #7	$115.53	9.680%	$126.7133	$126.71	$126.70	$126.70
7 purchase totals =	$734.27		$797.3906	$797.39	$797.35	$797.50