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	$39.49	3.275%	$40.7833	$40.78	$40.80	$40.80
Purchase #2	$106.25	4.684%	$111.2268	$111.23	$111.25	$111.20
Purchase #3	$163.40	13.370%	$185.2466	$185.25	$185.25	$185.20
Purchase #4	$162.80	11.444%	$181.4308	$181.43	$181.45	$181.40
Purchase #5	$39.87	11.247%	$44.3542	$44.35	$44.35	$44.40
Purchase #6	$65.63	8.246%	$71.0418	$71.04	$71.05	$71.00
Purchase #7	$228.80	13.404%	$259.4684	$259.47	$259.45	$259.50
7 purchase totals =	$806.24		$893.5519	$893.55	$893.60	$893.50