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	$143.55	7.476%	$154.2818	$154.28	$154.30	$154.30
Purchase #2	$127.91	13.732%	$145.4746	$145.47	$145.45	$145.50
Purchase #3	$18.90	5.223%	$19.8871	$19.89	$19.90	$19.90
Purchase #4	$30.49	5.668%	$32.2182	$32.22	$32.20	$32.20
Purchase #5	$43.66	4.260%	$45.5199	$45.52	$45.50	$45.50
Purchase #6	$91.58	9.755%	$100.5136	$100.51	$100.50	$100.50
Purchase #7	$145.56	5.134%	$153.0331	$153.03	$153.05	$153.00
7 purchase totals =	$601.65		$650.9283	$650.92	$650.90	$650.90