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	$11.84	7.382%	$12.714	$12.71	$12.70	$12.70
Purchase #2	$86.64	13.841%	$98.6318	$98.63	$98.65	$98.60
Purchase #3	$85.78	3.645%	$88.9067	$88.91	$88.90	$88.90
Purchase #4	$112.32	13.806%	$127.8269	$127.83	$127.85	$127.80
Purchase #5	$234.38	3.730%	$243.1224	$243.12	$243.10	$243.10
Purchase #6	$187.58	13.475%	$212.8564	$212.86	$212.85	$212.90
Purchase #7	$119.65	5.759%	$126.5406	$126.54	$126.55	$126.50
7 purchase totals =	$838.19		$910.5988	$910.60	$910.60	$910.50