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	$160.27	8.253%	$173.4971	$173.50	$173.50	$173.50
Purchase #2	$119.63	12.184%	$134.2057	$134.21	$134.20	$134.20
Purchase #3	$10.91	13.109%	$12.3402	$12.34	$12.35	$12.30
Purchase #4	$157.83	11.869%	$176.5628	$176.56	$176.55	$176.60
Purchase #5	$25.60	11.199%	$28.4669	$28.47	$28.45	$28.50
Purchase #6	$104.52	3.794%	$108.4855	$108.49	$108.50	$108.50
Purchase #7	$80.44	12.448%	$90.4532	$90.45	$90.45	$90.50
7 purchase totals =	$659.20		$724.0114	$724.02	$724.00	$724.10