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	$89.60	13.522%	$101.7157	$101.72	$101.70	$101.70
Purchase #2	$103.68	7.298%	$111.2466	$111.25	$111.25	$111.20
Purchase #3	$164.32	7.330%	$176.3647	$176.36	$176.35	$176.40
Purchase #4	$145.77	12.591%	$164.1239	$164.12	$164.10	$164.10
Purchase #5	$19.55	10.570%	$21.6164	$21.62	$21.60	$21.60
Purchase #6	$59.93	13.336%	$67.9223	$67.92	$67.90	$67.90
Purchase #7	$34.81	8.677%	$37.8305	$37.83	$37.85	$37.80
7 purchase totals =	$617.66		$680.8201	$680.82	$680.75	$680.70