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	$146.91	9.749%	$161.2323	$161.23	$161.25	$161.20
Purchase #2	$229.25	13.639%	$260.5174	$260.52	$260.50	$260.50
Purchase #3	$137.64	12.530%	$154.8863	$154.89	$154.90	$154.90
Purchase #4	$118.27	7.435%	$127.0634	$127.06	$127.05	$127.10
Purchase #5	$18.73	10.489%	$20.6946	$20.69	$20.70	$20.70
Purchase #6	$44.76	7.672%	$48.194	$48.19	$48.20	$48.20
Purchase #7	$21.33	11.858%	$23.8593	$23.86	$23.85	$23.90
7 purchase totals =	$716.89		$796.4473	$796.44	$796.45	$796.50