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	$121.99	4.535%	$127.5222	$127.52	$127.50	$127.50
Purchase #2	$155.31	10.679%	$171.8956	$171.90	$171.90	$171.90
Purchase #3	$12.73	7.247%	$13.6525	$13.65	$13.65	$13.70
Purchase #4	$78.43	6.109%	$83.2213	$83.22	$83.20	$83.20
Purchase #5	$13.94	13.541%	$15.8276	$15.83	$15.85	$15.80
Purchase #6	$12.42	9.352%	$13.5815	$13.58	$13.60	$13.60
Purchase #7	$109.98	13.256%	$124.5589	$124.56	$124.55	$124.60
7 purchase totals =	$504.80		$550.2596	$550.26	$550.25	$550.30