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	$19.52	3.658%	$20.234	$20.23	$20.25	$20.20
Purchase #2	$21.64	6.500%	$23.0466	$23.05	$23.05	$23.00
Purchase #3	$13.48	5.462%	$14.2163	$14.22	$14.20	$14.20
Purchase #4	$95.76	4.831%	$100.3862	$100.39	$100.40	$100.40
Purchase #5	$163.48	4.823%	$171.3646	$171.36	$171.35	$171.40
Purchase #6	$18.92	13.648%	$21.5022	$21.50	$21.50	$21.50
Purchase #7	$113.71	11.756%	$127.0777	$127.08	$127.10	$127.10
7 purchase totals =	$446.51		$477.8276	$477.83	$477.85	$477.80