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	$144.25	6.266%	$153.2887	$153.29	$153.30	$153.30
Purchase #2	$45.79	10.174%	$50.4487	$50.45	$50.45	$50.40
Purchase #3	$139.72	9.603%	$153.1373	$153.14	$153.15	$153.10
Purchase #4	$221.65	13.629%	$251.8587	$251.86	$251.85	$251.90
Purchase #5	$75.74	3.117%	$78.1008	$78.10	$78.10	$78.10
Purchase #6	$12.41	12.697%	$13.9857	$13.99	$14.00	$14.00
Purchase #7	$127.88	11.437%	$142.5056	$142.51	$142.50	$142.50
7 purchase totals =	$767.44		$843.3255	$843.34	$843.35	$843.30