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	$38.38	5.556%	$40.5124	$40.51	$40.50	$40.50
Purchase #2	$120.95	8.161%	$130.8207	$130.82	$130.80	$130.80
Purchase #3	$238.35	3.177%	$245.9224	$245.92	$245.90	$245.90
Purchase #4	$102.52	11.444%	$114.2524	$114.25	$114.25	$114.30
Purchase #5	$113.30	7.705%	$122.0298	$122.03	$122.05	$122.00
Purchase #6	$240.59	4.123%	$250.5095	$250.51	$250.50	$250.50
Purchase #7	$158.97	4.155%	$165.5752	$165.58	$165.60	$165.60
7 purchase totals =	$1,013.06		$1,069.6224	$1,069.62	$1,069.60	$1,069.60