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	$110.29	11.638%	$123.1256	$123.13	$123.15	$123.10
Purchase #2	$78.95	7.838%	$85.1381	$85.14	$85.15	$85.10
Purchase #3	$158.61	9.195%	$173.1942	$173.19	$173.20	$173.20
Purchase #4	$45.54	9.821%	$50.0125	$50.01	$50.00	$50.00
Purchase #5	$128.29	12.606%	$144.4622	$144.46	$144.45	$144.50
Purchase #6	$54.65	7.798%	$58.9116	$58.91	$58.90	$58.90
Purchase #7	$239.34	6.856%	$255.7492	$255.75	$255.75	$255.70
7 purchase totals =	$815.67		$890.5934	$890.59	$890.60	$890.50