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	$139.71	11.288%	$155.4805	$155.48	$155.50	$155.50
Purchase #2	$140.41	4.654%	$146.9447	$146.94	$146.95	$146.90
Purchase #3	$159.56	13.811%	$181.5968	$181.60	$181.60	$181.60
Purchase #4	$66.27	6.852%	$70.8108	$70.81	$70.80	$70.80
Purchase #5	$166.58	7.754%	$179.4966	$179.50	$179.50	$179.50
Purchase #6	$26.87	5.188%	$28.264	$28.26	$28.25	$28.30
Purchase #7	$244.87	3.334%	$253.034	$253.03	$253.05	$253.00
7 purchase totals =	$944.27		$1,015.6274	$1,015.62	$1,015.65	$1,015.60