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	$46.62	13.485%	$52.9067	$52.91	$52.90	$52.90
Purchase #2	$144.43	13.868%	$164.4596	$164.46	$164.45	$164.50
Purchase #3	$90.53	12.266%	$101.6344	$101.63	$101.65	$101.60
Purchase #4	$243.95	13.152%	$276.0343	$276.03	$276.05	$276.00
Purchase #5	$38.74	6.588%	$41.2922	$41.29	$41.30	$41.30
Purchase #6	$101.26	10.481%	$111.8731	$111.87	$111.85	$111.90
Purchase #7	$139.58	4.531%	$145.9044	$145.90	$145.90	$145.90
7 purchase totals =	$805.11		$894.1047	$894.09	$894.10	$894.10