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	$136.52	10.311%	$150.5966	$150.60	$150.60	$150.60
Purchase #2	$193.46	13.116%	$218.8342	$218.83	$218.85	$218.80
Purchase #3	$47.56	7.105%	$50.9391	$50.94	$50.95	$50.90
Purchase #4	$9.54	7.621%	$10.267	$10.27	$10.25	$10.30
Purchase #5	$144.66	9.518%	$158.4287	$158.43	$158.45	$158.40
Purchase #6	$229.91	5.746%	$243.1206	$243.12	$243.10	$243.10
Purchase #7	$97.71	6.847%	$104.4002	$104.40	$104.40	$104.40
7 purchase totals =	$859.36		$936.5864	$936.59	$936.60	$936.50