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	$97.57	12.636%	$109.8989	$109.90	$109.90	$109.90
Purchase #2	$226.68	10.219%	$249.8444	$249.84	$249.85	$249.80
Purchase #3	$244.46	4.523%	$255.5169	$255.52	$255.50	$255.50
Purchase #4	$76.95	4.157%	$80.1488	$80.15	$80.15	$80.10
Purchase #5	$45.77	5.644%	$48.3533	$48.35	$48.35	$48.40
Purchase #6	$130.71	10.494%	$144.4267	$144.43	$144.45	$144.40
Purchase #7	$221.80	3.205%	$228.9087	$228.91	$228.90	$228.90
7 purchase totals =	$1,043.94		$1,117.0977	$1,117.10	$1,117.10	$1,117.00