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	$25.62	10.462%	$28.3004	$28.30	$28.30	$28.30
Purchase #2	$113.91	8.771%	$123.901	$123.90	$123.90	$123.90
Purchase #3	$47.49	6.377%	$50.5184	$50.52	$50.50	$50.50
Purchase #4	$60.61	5.800%	$64.1254	$64.13	$64.15	$64.10
Purchase #5	$79.58	13.286%	$90.153	$90.15	$90.15	$90.20
Purchase #6	$52.25	9.836%	$57.3893	$57.39	$57.40	$57.40
Purchase #7	$221.31	6.527%	$235.7549	$235.75	$235.75	$235.80
7 purchase totals =	$600.77		$650.1424	$650.14	$650.15	$650.20