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	$170.56	9.866%	$187.3874	$187.39	$187.40	$187.40
Purchase #2	$53.31	13.534%	$60.525	$60.53	$60.55	$60.50
Purchase #3	$40.70	12.152%	$45.6459	$45.65	$45.65	$45.60
Purchase #4	$111.93	12.792%	$126.2481	$126.25	$126.25	$126.20
Purchase #5	$172.92	13.791%	$196.7674	$196.77	$196.75	$196.80
Purchase #6	$192.34	5.867%	$203.6246	$203.62	$203.60	$203.60
Purchase #7	$19.71	5.837%	$20.8605	$20.86	$20.85	$20.90
7 purchase totals =	$761.47		$841.0589	$841.07	$841.05	$841.00