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	$138.56	9.112%	$151.1856	$151.19	$151.20	$151.20
Purchase #2	$138.62	4.229%	$144.4822	$144.48	$144.50	$144.50
Purchase #3	$20.51	11.766%	$22.9232	$22.92	$22.90	$22.90
Purchase #4	$193.72	12.863%	$218.6382	$218.64	$218.65	$218.60
Purchase #5	$241.90	5.469%	$255.1295	$255.13	$255.15	$255.10
Purchase #6	$75.53	13.747%	$85.9131	$85.91	$85.90	$85.90
Purchase #7	$200.35	9.788%	$219.9603	$219.96	$219.95	$220.00
7 purchase totals =	$1,009.19		$1,098.2321	$1,098.23	$1,098.25	$1,098.20