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	$230.93	6.559%	$246.0767	$246.08	$246.10	$246.10
Purchase #2	$228.55	4.227%	$238.2108	$238.21	$238.20	$238.20
Purchase #3	$116.25	10.770%	$128.7701	$128.77	$128.75	$128.80
Purchase #4	$222.31	7.250%	$238.4275	$238.43	$238.45	$238.40
Purchase #5	$86.77	3.717%	$89.9952	$90.00	$90.00	$90.00
Purchase #6	$228.48	5.858%	$241.8644	$241.86	$241.85	$241.90
Purchase #7	$171.61	8.269%	$185.8004	$185.80	$185.80	$185.80
7 purchase totals =	$1,284.90		$1,369.1451	$1,369.15	$1,369.15	$1,369.20