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	$123.65	5.580%	$130.5497	$130.55	$130.55	$130.50
Purchase #2	$109.52	10.639%	$121.1718	$121.17	$121.15	$121.20
Purchase #3	$162.62	10.634%	$179.913	$179.91	$179.90	$179.90
Purchase #4	$59.45	12.452%	$66.8527	$66.85	$66.85	$66.90
Purchase #5	$136.42	6.621%	$145.4524	$145.45	$145.45	$145.50
Purchase #6	$122.51	5.416%	$129.1451	$129.15	$129.15	$129.10
Purchase #7	$43.43	4.815%	$45.5212	$45.52	$45.50	$45.50
7 purchase totals =	$757.60		$818.6059	$818.60	$818.55	$818.60