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	$30.52	10.105%	$33.604	$33.60	$33.60	$33.60
Purchase #2	$229.60	13.300%	$260.1368	$260.14	$260.15	$260.10
Purchase #3	$131.93	5.700%	$139.45	$139.45	$139.45	$139.50
Purchase #4	$208.91	11.237%	$232.3852	$232.39	$232.40	$232.40
Purchase #5	$75.92	4.779%	$79.5482	$79.55	$79.55	$79.50
Purchase #6	$115.28	7.492%	$123.9168	$123.92	$123.90	$123.90
Purchase #7	$164.65	13.719%	$187.2383	$187.24	$187.25	$187.20
7 purchase totals =	$956.81		$1,056.2793	$1,056.29	$1,056.30	$1,056.20