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	$157.50	4.186%	$164.093	$164.09	$164.10	$164.10
Purchase #2	$52.77	6.586%	$56.2454	$56.25	$56.25	$56.20
Purchase #3	$108.49	4.725%	$113.6162	$113.62	$113.60	$113.60
Purchase #4	$172.33	8.209%	$186.4766	$186.48	$186.50	$186.50
Purchase #5	$29.55	11.139%	$32.8416	$32.84	$32.85	$32.80
Purchase #6	$111.54	4.487%	$116.5448	$116.54	$116.55	$116.50
Purchase #7	$124.28	13.242%	$140.7372	$140.74	$140.75	$140.70
7 purchase totals =	$756.46		$810.5548	$810.56	$810.60	$810.40