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	$50.85	13.213%	$57.5688	$57.57	$57.55	$57.60
Purchase #2	$210.64	9.586%	$230.832	$230.83	$230.85	$230.80
Purchase #3	$107.61	3.727%	$111.6206	$111.62	$111.60	$111.60
Purchase #4	$150.28	8.742%	$163.4175	$163.42	$163.40	$163.40
Purchase #5	$98.58	12.761%	$111.1598	$111.16	$111.15	$111.20
Purchase #6	$151.30	3.390%	$156.4291	$156.43	$156.45	$156.40
Purchase #7	$246.47	3.205%	$254.3694	$254.37	$254.35	$254.40
7 purchase totals =	$1,015.73		$1,085.3972	$1,085.40	$1,085.35	$1,085.40