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	$94.57	13.274%	$107.1232	$107.12	$107.10	$107.10
Purchase #2	$123.27	12.125%	$138.2165	$138.22	$138.20	$138.20
Purchase #3	$109.34	3.320%	$112.9701	$112.97	$112.95	$113.00
Purchase #4	$95.29	10.859%	$105.6375	$105.64	$105.65	$105.60
Purchase #5	$29.74	12.140%	$33.3504	$33.35	$33.35	$33.40
Purchase #6	$216.76	6.826%	$231.556	$231.56	$231.55	$231.60
Purchase #7	$73.85	6.686%	$78.7876	$78.79	$78.80	$78.80
7 purchase totals =	$742.82		$807.6413	$807.65	$807.60	$807.70