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	$164.36	5.558%	$173.4951	$173.50	$173.50	$173.50
Purchase #2	$140.43	13.344%	$159.169	$159.17	$159.15	$159.20
Purchase #3	$79.72	3.588%	$82.5804	$82.58	$82.60	$82.60
Purchase #4	$65.29	8.394%	$70.7704	$70.77	$70.75	$70.80
Purchase #5	$54.85	7.855%	$59.1585	$59.16	$59.15	$59.20
Purchase #6	$237.84	7.592%	$255.8968	$255.90	$255.90	$255.90
Purchase #7	$69.81	12.117%	$78.2689	$78.27	$78.25	$78.30
7 purchase totals =	$812.30		$879.3391	$879.35	$879.30	$879.50