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	$63.34	4.396%	$66.1244	$66.12	$66.10	$66.10
Purchase #2	$250.97	12.672%	$282.7729	$282.77	$282.75	$282.80
Purchase #3	$243.96	11.268%	$271.4494	$271.45	$271.45	$271.40
Purchase #4	$45.76	10.525%	$50.5762	$50.58	$50.60	$50.60
Purchase #5	$226.50	11.142%	$251.7366	$251.74	$251.75	$251.70
Purchase #6	$112.99	10.187%	$124.5003	$124.50	$124.50	$124.50
Purchase #7	$37.91	11.584%	$42.3015	$42.30	$42.30	$42.30
7 purchase totals =	$981.43		$1,089.4613	$1,089.46	$1,089.45	$1,089.40