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	$248.43	3.283%	$256.586	$256.59	$256.60	$256.60
Purchase #2	$145.39	6.724%	$155.166	$155.17	$155.15	$155.20
Purchase #3	$140.36	11.588%	$156.6249	$156.62	$156.60	$156.60
Purchase #4	$70.61	3.162%	$72.8427	$72.84	$72.85	$72.80
Purchase #5	$164.99	11.610%	$184.1453	$184.15	$184.15	$184.10
Purchase #6	$19.64	5.634%	$20.7465	$20.75	$20.75	$20.70
Purchase #7	$49.53	7.601%	$53.2948	$53.29	$53.30	$53.30
7 purchase totals =	$838.95		$899.4062	$899.41	$899.40	$899.30