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	$48.47	8.640%	$52.6578	$52.66	$52.65	$52.70
Purchase #2	$223.33	11.419%	$248.8321	$248.83	$248.85	$248.80
Purchase #3	$45.92	9.147%	$50.1203	$50.12	$50.10	$50.10
Purchase #4	$212.39	13.332%	$240.7058	$240.71	$240.70	$240.70
Purchase #5	$206.77	10.198%	$227.8564	$227.86	$227.85	$227.90
Purchase #6	$97.30	7.189%	$104.2949	$104.29	$104.30	$104.30
Purchase #7	$166.52	7.534%	$179.0656	$179.07	$179.05	$179.10
7 purchase totals =	$1,000.70		$1,103.5329	$1,103.54	$1,103.50	$1,103.60