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	$248.30	4.131%	$258.5573	$258.56	$258.55	$258.60
Purchase #2	$82.30	10.348%	$90.8164	$90.82	$90.80	$90.80
Purchase #3	$130.35	6.316%	$138.5829	$138.58	$138.60	$138.60
Purchase #4	$87.42	3.137%	$90.1624	$90.16	$90.15	$90.20
Purchase #5	$42.95	12.667%	$48.3905	$48.39	$48.40	$48.40
Purchase #6	$22.82	10.430%	$25.2001	$25.20	$25.20	$25.20
Purchase #7	$241.65	12.762%	$272.4894	$272.49	$272.50	$272.50
7 purchase totals =	$855.79		$924.1990	$924.20	$924.20	$924.30