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	$171.90	7.109%	$184.1204	$184.12	$184.10	$184.10
Purchase #2	$90.50	10.419%	$99.9292	$99.93	$99.95	$99.90
Purchase #3	$105.35	11.357%	$117.3146	$117.31	$117.30	$117.30
Purchase #4	$122.26	4.662%	$127.9598	$127.96	$127.95	$128.00
Purchase #5	$70.49	13.586%	$80.0668	$80.07	$80.05	$80.10
Purchase #6	$132.72	10.308%	$146.4008	$146.40	$146.40	$146.40
Purchase #7	$127.73	9.268%	$139.568	$139.57	$139.55	$139.60
7 purchase totals =	$820.95		$895.3596	$895.36	$895.30	$895.40