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	$38.28	4.103%	$39.8506	$39.85	$39.85	$39.90
Purchase #2	$29.32	3.409%	$30.3195	$30.32	$30.30	$30.30
Purchase #3	$41.55	10.175%	$45.7777	$45.78	$45.80	$45.80
Purchase #4	$242.29	4.771%	$253.8497	$253.85	$253.85	$253.80
Purchase #5	$166.32	10.116%	$183.1449	$183.14	$183.15	$183.10
Purchase #6	$86.40	9.367%	$94.4931	$94.49	$94.50	$94.50
Purchase #7	$33.57	10.853%	$37.2134	$37.21	$37.20	$37.20
7 purchase totals =	$637.73		$684.6489	$684.64	$684.65	$684.60