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	$137.36	13.290%	$155.6151	$155.62	$155.60	$155.60
Purchase #2	$161.68	10.141%	$178.076	$178.08	$178.10	$178.10
Purchase #3	$90.58	10.464%	$100.0583	$100.06	$100.05	$100.10
Purchase #4	$172.85	12.584%	$194.6014	$194.60	$194.60	$194.60
Purchase #5	$117.56	12.152%	$131.8459	$131.85	$131.85	$131.80
Purchase #6	$20.38	10.768%	$22.5745	$22.57	$22.55	$22.60
Purchase #7	$124.94	7.146%	$133.8682	$133.87	$133.85	$133.90
7 purchase totals =	$825.35		$916.6394	$916.65	$916.60	$916.70