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	$35.90	12.208%	$40.2827	$40.28	$40.30	$40.30
Purchase #2	$11.93	9.354%	$13.0459	$13.05	$13.05	$13.00
Purchase #3	$96.33	7.134%	$103.2022	$103.20	$103.20	$103.20
Purchase #4	$111.43	13.551%	$126.5299	$126.53	$126.55	$126.50
Purchase #5	$138.97	11.773%	$155.3309	$155.33	$155.35	$155.30
Purchase #6	$102.65	8.741%	$111.6226	$111.62	$111.60	$111.60
Purchase #7	$82.78	3.171%	$85.405	$85.41	$85.40	$85.40
7 purchase totals =	$579.99		$635.4192	$635.42	$635.45	$635.30