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	$37.45	13.443%	$42.4844	$42.48	$42.50	$42.50
Purchase #2	$108.99	8.625%	$118.3904	$118.39	$118.40	$118.40
Purchase #3	$243.32	13.306%	$275.6962	$275.70	$275.70	$275.70
Purchase #4	$49.73	5.566%	$52.498	$52.50	$52.50	$52.50
Purchase #5	$207.52	4.156%	$216.1445	$216.14	$216.15	$216.10
Purchase #6	$188.64	12.654%	$212.5105	$212.51	$212.50	$212.50
Purchase #7	$241.25	5.593%	$254.7431	$254.74	$254.75	$254.70
7 purchase totals =	$1,076.90		$1,172.4671	$1,172.46	$1,172.50	$1,172.40