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	$226.90	12.731%	$255.7866	$255.79	$255.80	$255.80
Purchase #2	$158.65	5.638%	$167.5947	$167.59	$167.60	$167.60
Purchase #3	$14.66	3.459%	$15.1671	$15.17	$15.15	$15.20
Purchase #4	$82.75	4.495%	$86.4696	$86.47	$86.45	$86.50
Purchase #5	$34.83	5.203%	$36.6422	$36.64	$36.65	$36.60
Purchase #6	$168.64	10.812%	$186.8734	$186.87	$186.85	$186.90
Purchase #7	$46.68	13.699%	$53.0747	$53.07	$53.05	$53.10
7 purchase totals =	$733.11		$801.6083	$801.60	$801.55	$801.70