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	$188.42	13.738%	$214.3051	$214.31	$214.30	$214.30
Purchase #2	$139.81	4.864%	$146.6104	$146.61	$146.60	$146.60
Purchase #3	$246.59	10.638%	$272.8222	$272.82	$272.80	$272.80
Purchase #4	$91.67	13.699%	$104.2279	$104.23	$104.25	$104.20
Purchase #5	$145.27	10.284%	$160.2096	$160.21	$160.20	$160.20
Purchase #6	$131.92	8.520%	$143.1596	$143.16	$143.15	$143.20
Purchase #7	$59.82	3.663%	$62.0112	$62.01	$62.00	$62.00
7 purchase totals =	$1,003.50		$1,103.3460	$1,103.35	$1,103.30	$1,103.30