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	$103.36	7.802%	$111.4241	$111.42	$111.40	$111.40
Purchase #2	$62.80	11.760%	$70.1853	$70.19	$70.20	$70.20
Purchase #3	$38.64	5.576%	$40.7946	$40.79	$40.80	$40.80
Purchase #4	$145.88	9.215%	$159.3228	$159.32	$159.30	$159.30
Purchase #5	$32.47	10.201%	$35.7823	$35.78	$35.80	$35.80
Purchase #6	$127.98	11.764%	$143.0356	$143.04	$143.05	$143.00
Purchase #7	$126.34	3.748%	$131.0752	$131.08	$131.10	$131.10
7 purchase totals =	$637.47		$691.6199	$691.62	$691.65	$691.60