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	$127.34	9.376%	$139.2794	$139.28	$139.30	$139.30
Purchase #2	$101.31	10.191%	$111.6345	$111.63	$111.65	$111.60
Purchase #3	$143.77	6.153%	$152.6162	$152.62	$152.60	$152.60
Purchase #4	$111.62	5.496%	$117.7546	$117.75	$117.75	$117.80
Purchase #5	$184.94	6.317%	$196.6227	$196.62	$196.60	$196.60
Purchase #6	$240.67	9.871%	$264.4265	$264.43	$264.45	$264.40
Purchase #7	$21.87	7.332%	$23.4735	$23.47	$23.45	$23.50
7 purchase totals =	$931.52		$1,005.8074	$1,005.80	$1,005.80	$1,005.80