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	$91.72	9.365%	$100.3096	$100.31	$100.30	$100.30
Purchase #2	$11.63	4.821%	$12.1907	$12.19	$12.20	$12.20
Purchase #3	$98.49	4.696%	$103.1151	$103.12	$103.10	$103.10
Purchase #4	$150.39	10.763%	$166.5765	$166.58	$166.60	$166.60
Purchase #5	$178.35	12.658%	$200.9255	$200.93	$200.95	$200.90
Purchase #6	$174.53	8.433%	$189.2481	$189.25	$189.25	$189.20
Purchase #7	$129.84	11.267%	$144.4691	$144.47	$144.45	$144.50
7 purchase totals =	$834.95		$916.8346	$916.85	$916.85	$916.80