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	$240.25	6.196%	$255.1359	$255.14	$255.15	$255.10
Purchase #2	$32.42	10.828%	$35.9304	$35.93	$35.95	$35.90
Purchase #3	$50.70	10.629%	$56.0889	$56.09	$56.10	$56.10
Purchase #4	$134.27	9.310%	$146.7705	$146.77	$146.75	$146.80
Purchase #5	$45.90	9.420%	$50.2238	$50.22	$50.20	$50.20
Purchase #6	$66.31	8.148%	$71.7129	$71.71	$71.70	$71.70
Purchase #7	$216.68	7.665%	$233.2885	$233.29	$233.30	$233.30
7 purchase totals =	$786.53		$849.1509	$849.15	$849.15	$849.10