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	$12.48	9.754%	$13.6973	$13.70	$13.70	$13.70
Purchase #2	$133.30	9.605%	$146.1035	$146.10	$146.10	$146.10
Purchase #3	$246.34	7.574%	$264.9978	$265.00	$265.00	$265.00
Purchase #4	$123.91	5.510%	$130.7374	$130.74	$130.75	$130.70
Purchase #5	$123.30	3.200%	$127.2456	$127.25	$127.25	$127.20
Purchase #6	$88.78	12.428%	$99.8136	$99.81	$99.80	$99.80
Purchase #7	$152.41	4.283%	$158.9377	$158.94	$158.95	$158.90
7 purchase totals =	$880.52		$941.5329	$941.54	$941.55	$941.40