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	$145.96	3.345%	$150.8424	$150.84	$150.85	$150.80
Purchase #2	$111.71	10.422%	$123.3524	$123.35	$123.35	$123.40
Purchase #3	$242.64	9.542%	$265.7927	$265.79	$265.80	$265.80
Purchase #4	$101.86	9.196%	$111.227	$111.23	$111.25	$111.20
Purchase #5	$122.52	10.785%	$135.7338	$135.73	$135.75	$135.70
Purchase #6	$62.64	6.160%	$66.4986	$66.50	$66.50	$66.50
Purchase #7	$46.91	3.469%	$48.5373	$48.54	$48.55	$48.50
7 purchase totals =	$834.24		$901.9842	$901.98	$902.05	$901.90