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	$180.72	4.680%	$189.1777	$189.18	$189.20	$189.20
Purchase #2	$91.77	9.752%	$100.7194	$100.72	$100.70	$100.70
Purchase #3	$230.50	3.351%	$238.2241	$238.22	$238.20	$238.20
Purchase #4	$248.59	6.541%	$264.8503	$264.85	$264.85	$264.90
Purchase #5	$168.82	8.412%	$183.0211	$183.02	$183.00	$183.00
Purchase #6	$133.61	6.613%	$142.4456	$142.45	$142.45	$142.40
Purchase #7	$87.39	5.329%	$92.047	$92.05	$92.05	$92.00
7 purchase totals =	$1,141.40		$1,210.4852	$1,210.49	$1,210.45	$1,210.40