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	$138.75	13.523%	$157.5132	$157.51	$157.50	$157.50
Purchase #2	$67.53	6.468%	$71.8978	$71.90	$71.90	$71.90
Purchase #3	$185.87	5.775%	$196.604	$196.60	$196.60	$196.60
Purchase #4	$94.50	5.634%	$99.8241	$99.82	$99.80	$99.80
Purchase #5	$244.31	4.337%	$254.9057	$254.91	$254.90	$254.90
Purchase #6	$239.55	6.719%	$255.6454	$255.65	$255.65	$255.60
Purchase #7	$247.47	11.669%	$276.3473	$276.35	$276.35	$276.30
7 purchase totals =	$1,217.98		$1,312.7375	$1,312.74	$1,312.70	$1,312.60