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	$240.73	13.473%	$273.1636	$273.16	$273.15	$273.20
Purchase #2	$230.30	13.870%	$262.2426	$262.24	$262.25	$262.20
Purchase #3	$74.46	5.149%	$78.2939	$78.29	$78.30	$78.30
Purchase #4	$249.60	10.358%	$275.4536	$275.45	$275.45	$275.50
Purchase #5	$19.41	9.768%	$21.306	$21.31	$21.30	$21.30
Purchase #6	$122.47	6.815%	$130.8163	$130.82	$130.80	$130.80
Purchase #7	$112.45	3.372%	$116.2418	$116.24	$116.25	$116.20
7 purchase totals =	$1,049.42		$1,157.5178	$1,157.51	$1,157.50	$1,157.50