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	$145.59	7.197%	$156.0681	$156.07	$156.05	$156.10
Purchase #2	$228.61	11.747%	$255.4648	$255.46	$255.45	$255.50
Purchase #3	$123.48	4.470%	$128.9996	$129.00	$129.00	$129.00
Purchase #4	$137.37	5.867%	$145.4295	$145.43	$145.45	$145.40
Purchase #5	$75.77	12.706%	$85.3973	$85.40	$85.40	$85.40
Purchase #6	$12.31	9.302%	$13.4551	$13.46	$13.45	$13.50
Purchase #7	$99.55	4.572%	$104.1014	$104.10	$104.10	$104.10
7 purchase totals =	$822.68		$888.9158	$888.92	$888.90	$889.00