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	$35.70	13.672%	$40.5809	$40.58	$40.60	$40.60
Purchase #2	$235.51	12.636%	$265.269	$265.27	$265.25	$265.30
Purchase #3	$241.87	8.777%	$263.0989	$263.10	$263.10	$263.10
Purchase #4	$30.28	3.224%	$31.2562	$31.26	$31.25	$31.30
Purchase #5	$40.51	6.710%	$43.2282	$43.23	$43.25	$43.20
Purchase #6	$244.80	9.304%	$267.5762	$267.58	$267.60	$267.60
Purchase #7	$160.47	7.340%	$172.2485	$172.25	$172.25	$172.20
7 purchase totals =	$989.14		$1,083.2579	$1,083.27	$1,083.30	$1,083.30