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	$80.48	12.430%	$90.4837	$90.48	$90.50	$90.50
Purchase #2	$187.87	4.407%	$196.1494	$196.15	$196.15	$196.10
Purchase #3	$51.34	4.243%	$53.5184	$53.52	$53.50	$53.50
Purchase #4	$225.71	11.624%	$251.9465	$251.95	$251.95	$251.90
Purchase #5	$151.91	5.233%	$159.8595	$159.86	$159.85	$159.90
Purchase #6	$48.52	9.590%	$53.1731	$53.17	$53.15	$53.20
Purchase #7	$145.35	13.704%	$165.2688	$165.27	$165.25	$165.30
7 purchase totals =	$891.18		$970.3994	$970.40	$970.35	$970.40