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	$226.71	8.585%	$246.1731	$246.17	$246.15	$246.20
Purchase #2	$42.25	8.344%	$45.7753	$45.78	$45.80	$45.80
Purchase #3	$131.65	6.401%	$140.0769	$140.08	$140.10	$140.10
Purchase #4	$29.27	10.466%	$32.3334	$32.33	$32.35	$32.30
Purchase #5	$69.62	11.491%	$77.62	$77.62	$77.60	$77.60
Purchase #6	$64.83	9.838%	$71.208	$71.21	$71.20	$71.20
Purchase #7	$35.45	5.590%	$37.4317	$37.43	$37.45	$37.40
7 purchase totals =	$599.78		$650.6184	$650.62	$650.65	$650.60