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	$111.29	8.112%	$120.3178	$120.32	$120.30	$120.30
Purchase #2	$37.94	9.183%	$41.424	$41.42	$41.40	$41.40
Purchase #3	$95.53	10.809%	$105.8558	$105.86	$105.85	$105.90
Purchase #4	$130.40	5.110%	$137.0634	$137.06	$137.05	$137.10
Purchase #5	$244.43	3.779%	$253.667	$253.67	$253.65	$253.70
Purchase #6	$40.89	13.152%	$46.2679	$46.27	$46.25	$46.30
Purchase #7	$97.69	10.491%	$107.9387	$107.94	$107.95	$107.90
7 purchase totals =	$758.17		$812.5346	$812.54	$812.45	$812.60