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	$7.74	12.234%	$8.6869	$8.69	$8.70	$8.70
Purchase #2	$117.54	5.424%	$123.9154	$123.92	$123.90	$123.90
Purchase #3	$131.52	10.546%	$145.3901	$145.39	$145.40	$145.40
Purchase #4	$153.55	4.697%	$160.7622	$160.76	$160.75	$160.80
Purchase #5	$71.77	10.752%	$79.4867	$79.49	$79.50	$79.50
Purchase #6	$162.27	6.390%	$172.6391	$172.64	$172.65	$172.60
Purchase #7	$102.89	7.731%	$110.8444	$110.84	$110.85	$110.80
7 purchase totals =	$747.28		$801.7248	$801.73	$801.75	$801.70