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	$88.35	13.488%	$100.2666	$100.27	$100.25	$100.30
Purchase #2	$160.45	6.487%	$170.8584	$170.86	$170.85	$170.90
Purchase #3	$155.42	7.481%	$167.047	$167.05	$167.05	$167.00
Purchase #4	$66.25	8.680%	$72.0005	$72.00	$72.00	$72.00
Purchase #5	$117.35	10.461%	$129.626	$129.63	$129.65	$129.60
Purchase #6	$198.40	6.325%	$210.9488	$210.95	$210.95	$210.90
Purchase #7	$111.94	4.807%	$117.321	$117.32	$117.30	$117.30
7 purchase totals =	$898.16		$968.0683	$968.08	$968.05	$968.00