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	$154.79	3.111%	$159.6055	$159.61	$159.60	$159.60
Purchase #2	$76.44	7.487%	$82.1631	$82.16	$82.15	$82.20
Purchase #3	$29.34	7.554%	$31.5563	$31.56	$31.55	$31.60
Purchase #4	$195.85	9.547%	$214.5478	$214.55	$214.55	$214.50
Purchase #5	$136.92	10.472%	$151.2583	$151.26	$151.25	$151.30
Purchase #6	$115.92	4.199%	$120.7875	$120.79	$120.80	$120.80
Purchase #7	$229.43	13.551%	$260.5201	$260.52	$260.50	$260.50
7 purchase totals =	$938.69		$1,020.4386	$1,020.45	$1,020.40	$1,020.50