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	$48.53	10.501%	$53.6261	$53.63	$53.65	$53.60
Purchase #2	$129.33	13.559%	$146.8659	$146.87	$146.85	$146.90
Purchase #3	$131.99	6.854%	$141.0366	$141.04	$141.05	$141.00
Purchase #4	$71.47	13.540%	$81.147	$81.15	$81.15	$81.10
Purchase #5	$123.29	3.225%	$127.2661	$127.27	$127.25	$127.30
Purchase #6	$33.50	5.592%	$35.3733	$35.37	$35.35	$35.40
Purchase #7	$89.96	10.521%	$99.4247	$99.42	$99.40	$99.40
7 purchase totals =	$628.07		$684.7397	$684.75	$684.70	$684.70