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	$48.63	4.418%	$50.7785	$50.78	$50.80	$50.80
Purchase #2	$149.74	13.247%	$169.5761	$169.58	$169.60	$169.60
Purchase #3	$101.65	5.233%	$106.9693	$106.97	$106.95	$107.00
Purchase #4	$150.25	10.132%	$165.4733	$165.47	$165.45	$165.50
Purchase #5	$230.88	5.871%	$244.435	$244.44	$244.45	$244.40
Purchase #6	$249.56	3.712%	$258.8237	$258.82	$258.80	$258.80
Purchase #7	$78.70	4.639%	$82.3509	$82.35	$82.35	$82.40
7 purchase totals =	$1,009.41		$1,078.4068	$1,078.41	$1,078.40	$1,078.50