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	$196.26	6.535%	$209.0856	$209.09	$209.10	$209.10
Purchase #2	$119.36	12.132%	$133.8408	$133.84	$133.85	$133.80
Purchase #3	$119.72	6.275%	$127.2324	$127.23	$127.25	$127.20
Purchase #4	$91.77	12.723%	$103.4459	$103.45	$103.45	$103.40
Purchase #5	$46.48	4.323%	$48.4893	$48.49	$48.50	$48.50
Purchase #6	$111.59	13.204%	$126.3243	$126.32	$126.30	$126.30
Purchase #7	$107.50	13.630%	$122.1523	$122.15	$122.15	$122.20
7 purchase totals =	$792.68		$870.5706	$870.57	$870.60	$870.50