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	$230.34	9.592%	$252.4342	$252.43	$252.45	$252.40
Purchase #2	$207.99	5.476%	$219.3795	$219.38	$219.40	$219.40
Purchase #3	$224.76	13.639%	$255.415	$255.42	$255.40	$255.40
Purchase #4	$96.39	4.324%	$100.5579	$100.56	$100.55	$100.60
Purchase #5	$191.57	10.264%	$211.2327	$211.23	$211.25	$211.20
Purchase #6	$75.31	9.745%	$82.649	$82.65	$82.65	$82.60
Purchase #7	$200.79	8.666%	$218.1905	$218.19	$218.20	$218.20
7 purchase totals =	$1,227.15		$1,339.8588	$1,339.86	$1,339.90	$1,339.80