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	$127.30	13.344%	$144.2869	$144.29	$144.30	$144.30
Purchase #2	$115.74	13.824%	$131.7399	$131.74	$131.75	$131.70
Purchase #3	$26.34	11.625%	$29.402	$29.40	$29.40	$29.40
Purchase #4	$123.45	3.355%	$127.5917	$127.59	$127.60	$127.60
Purchase #5	$223.87	4.393%	$233.7046	$233.70	$233.70	$233.70
Purchase #6	$161.40	7.216%	$173.0466	$173.05	$173.05	$173.00
Purchase #7	$89.38	13.637%	$101.5688	$101.57	$101.55	$101.60
7 purchase totals =	$867.48		$941.3405	$941.34	$941.35	$941.30