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	$36.88	6.260%	$39.1887	$39.19	$39.20	$39.20
Purchase #2	$100.91	4.131%	$105.0786	$105.08	$105.10	$105.10
Purchase #3	$243.35	3.394%	$251.6093	$251.61	$251.60	$251.60
Purchase #4	$116.76	5.482%	$123.1608	$123.16	$123.15	$123.20
Purchase #5	$139.67	4.147%	$145.4621	$145.46	$145.45	$145.50
Purchase #6	$104.58	8.313%	$113.2737	$113.27	$113.25	$113.30
Purchase #7	$168.55	10.358%	$186.0084	$186.01	$186.00	$186.00
7 purchase totals =	$910.70		$963.7816	$963.78	$963.75	$963.90