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	$64.37	4.852%	$67.4932	$67.49	$67.50	$67.50
Purchase #2	$30.34	10.663%	$33.5752	$33.58	$33.60	$33.60
Purchase #3	$50.63	12.866%	$57.1441	$57.14	$57.15	$57.10
Purchase #4	$232.78	3.636%	$241.2439	$241.24	$241.25	$241.20
Purchase #5	$137.99	11.310%	$153.5967	$153.60	$153.60	$153.60
Purchase #6	$57.72	6.849%	$61.6732	$61.67	$61.65	$61.70
Purchase #7	$73.93	6.340%	$78.6172	$78.62	$78.60	$78.60
7 purchase totals =	$647.76		$693.3435	$693.34	$693.35	$693.30