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	$216.92	10.661%	$240.0458	$240.05	$240.05	$240.00
Purchase #2	$170.58	13.247%	$193.1767	$193.18	$193.20	$193.20
Purchase #3	$59.30	8.848%	$64.5469	$64.55	$64.55	$64.50
Purchase #4	$170.73	8.123%	$184.5984	$184.60	$184.60	$184.60
Purchase #5	$116.81	11.310%	$130.0212	$130.02	$130.00	$130.00
Purchase #6	$50.61	7.749%	$54.5318	$54.53	$54.55	$54.50
Purchase #7	$137.99	10.579%	$152.588	$152.59	$152.60	$152.60
7 purchase totals =	$922.94		$1,019.5088	$1,019.52	$1,019.55	$1,019.40