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	$178.88	6.363%	$190.2621	$190.26	$190.25	$190.30
Purchase #2	$174.29	8.223%	$188.6219	$188.62	$188.60	$188.60
Purchase #3	$49.48	10.832%	$54.8397	$54.84	$54.85	$54.80
Purchase #4	$72.97	12.609%	$82.1708	$82.17	$82.15	$82.20
Purchase #5	$34.91	7.856%	$37.6525	$37.65	$37.65	$37.70
Purchase #6	$131.34	12.873%	$148.2474	$148.25	$148.25	$148.20
Purchase #7	$107.99	3.351%	$111.6087	$111.61	$111.60	$111.60
7 purchase totals =	$749.86		$813.4031	$813.40	$813.35	$813.40