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	$104.58	5.451%	$110.2807	$110.28	$110.30	$110.30
Purchase #2	$147.68	10.231%	$162.7891	$162.79	$162.80	$162.80
Purchase #3	$9.83	13.625%	$11.1693	$11.17	$11.15	$11.20
Purchase #4	$177.47	7.394%	$190.5921	$190.59	$190.60	$190.60
Purchase #5	$99.35	12.588%	$111.8562	$111.86	$111.85	$111.90
Purchase #6	$45.40	13.675%	$51.6085	$51.61	$51.60	$51.60
Purchase #7	$117.82	11.394%	$131.2444	$131.24	$131.25	$131.20
7 purchase totals =	$702.13		$769.5403	$769.54	$769.55	$769.60