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	$93.26	9.211%	$101.8502	$101.85	$101.85	$101.90
Purchase #2	$104.29	6.757%	$111.3369	$111.34	$111.35	$111.30
Purchase #3	$94.92	7.262%	$101.8131	$101.81	$101.80	$101.80
Purchase #4	$38.47	13.189%	$43.5438	$43.54	$43.55	$43.50
Purchase #5	$90.58	10.731%	$100.3001	$100.30	$100.30	$100.30
Purchase #6	$112.88	3.848%	$117.2236	$117.22	$117.20	$117.20
Purchase #7	$70.30	7.602%	$75.6442	$75.64	$75.65	$75.60
7 purchase totals =	$604.70		$651.7119	$651.70	$651.70	$651.60