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	$49.46	10.203%	$54.5064	$54.51	$54.50	$54.50
Purchase #2	$118.38	7.822%	$127.6397	$127.64	$127.65	$127.60
Purchase #3	$137.58	9.476%	$150.6171	$150.62	$150.60	$150.60
Purchase #4	$13.53	9.295%	$14.7876	$14.79	$14.80	$14.80
Purchase #5	$9.93	12.605%	$11.1817	$11.18	$11.20	$11.20
Purchase #6	$108.65	8.559%	$117.9494	$117.95	$117.95	$117.90
Purchase #7	$154.62	11.346%	$172.1632	$172.16	$172.15	$172.20
7 purchase totals =	$592.15		$648.8451	$648.85	$648.85	$648.80