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	$214.56	11.734%	$239.7365	$239.74	$239.75	$239.70
Purchase #2	$224.55	6.627%	$239.4309	$239.43	$239.45	$239.40
Purchase #3	$242.48	9.155%	$264.679	$264.68	$264.70	$264.70
Purchase #4	$166.77	4.643%	$174.5131	$174.51	$174.50	$174.50
Purchase #5	$47.43	10.335%	$52.3319	$52.33	$52.35	$52.30
Purchase #6	$6.32	13.664%	$7.1836	$7.18	$7.20	$7.20
Purchase #7	$98.31	13.370%	$111.454	$111.45	$111.45	$111.50
7 purchase totals =	$1,000.42		$1,089.3290	$1,089.32	$1,089.40	$1,089.30