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	$233.57	3.715%	$242.2471	$242.25	$242.25	$242.20
Purchase #2	$139.92	8.858%	$152.3141	$152.31	$152.30	$152.30
Purchase #3	$42.81	5.346%	$45.0986	$45.10	$45.10	$45.10
Purchase #4	$186.31	5.211%	$196.0186	$196.02	$196.00	$196.00
Purchase #5	$230.99	13.467%	$262.0974	$262.10	$262.10	$262.10
Purchase #6	$10.66	4.638%	$11.1544	$11.15	$11.15	$11.20
Purchase #7	$47.64	5.182%	$50.1087	$50.11	$50.10	$50.10
7 purchase totals =	$891.90		$959.0389	$959.04	$959.00	$959.00