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	$90.78	9.328%	$99.248	$99.25	$99.25	$99.20
Purchase #2	$35.97	6.592%	$38.3411	$38.34	$38.35	$38.30
Purchase #3	$146.64	10.585%	$162.1618	$162.16	$162.15	$162.20
Purchase #4	$19.39	11.110%	$21.5442	$21.54	$21.55	$21.50
Purchase #5	$152.38	13.254%	$172.5764	$172.58	$172.60	$172.60
Purchase #6	$244.68	5.851%	$258.9962	$259.00	$259.00	$259.00
Purchase #7	$146.95	8.116%	$158.8765	$158.88	$158.90	$158.90
7 purchase totals =	$836.79		$911.7442	$911.75	$911.80	$911.70