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	$146.70	7.856%	$158.2248	$158.22	$158.20	$158.20
Purchase #2	$104.59	6.229%	$111.1049	$111.10	$111.10	$111.10
Purchase #3	$181.44	13.451%	$205.8455	$205.85	$205.85	$205.80
Purchase #4	$217.88	10.154%	$240.0035	$240.00	$240.00	$240.00
Purchase #5	$152.29	10.249%	$167.8982	$167.90	$167.90	$167.90
Purchase #6	$39.65	6.813%	$42.3514	$42.35	$42.35	$42.40
Purchase #7	$43.51	5.791%	$46.0297	$46.03	$46.05	$46.00
7 purchase totals =	$886.06		$971.4580	$971.45	$971.45	$971.40