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	$102.89	3.686%	$106.6825	$106.68	$106.70	$106.70
Purchase #2	$82.34	12.358%	$92.5156	$92.52	$92.50	$92.50
Purchase #3	$82.65	8.402%	$89.5943	$89.59	$89.60	$89.60
Purchase #4	$41.88	11.695%	$46.7779	$46.78	$46.80	$46.80
Purchase #5	$74.46	6.204%	$79.0795	$79.08	$79.10	$79.10
Purchase #6	$62.30	13.436%	$70.6706	$70.67	$70.65	$70.70
Purchase #7	$242.37	12.322%	$272.2348	$272.23	$272.25	$272.20
7 purchase totals =	$688.89		$757.5552	$757.55	$757.60	$757.60