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	$119.48	6.374%	$127.0957	$127.10	$127.10	$127.10
Purchase #2	$37.68	12.647%	$42.4454	$42.45	$42.45	$42.40
Purchase #3	$211.38	12.708%	$238.2422	$238.24	$238.25	$238.20
Purchase #4	$140.72	12.447%	$158.2354	$158.24	$158.25	$158.20
Purchase #5	$111.68	12.796%	$125.9706	$125.97	$125.95	$126.00
Purchase #6	$169.95	8.131%	$183.7686	$183.77	$183.75	$183.80
Purchase #7	$39.80	13.273%	$45.0827	$45.08	$45.10	$45.10
7 purchase totals =	$830.69		$920.8406	$920.85	$920.85	$920.80