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	$16.94	6.652%	$18.0668	$18.07	$18.05	$18.10
Purchase #2	$142.91	5.855%	$151.2774	$151.28	$151.30	$151.30
Purchase #3	$161.42	3.253%	$166.671	$166.67	$166.65	$166.70
Purchase #4	$25.65	3.243%	$26.4818	$26.48	$26.50	$26.50
Purchase #5	$133.50	4.146%	$139.0349	$139.03	$139.05	$139.00
Purchase #6	$130.54	9.506%	$142.9491	$142.95	$142.95	$142.90
Purchase #7	$99.74	12.128%	$111.8365	$111.84	$111.85	$111.80
7 purchase totals =	$710.70		$756.3175	$756.32	$756.35	$756.30