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	$60.72	7.699%	$65.3948	$65.39	$65.40	$65.40
Purchase #2	$237.88	4.769%	$249.2245	$249.22	$249.20	$249.20
Purchase #3	$242.73	12.249%	$272.462	$272.46	$272.45	$272.50
Purchase #4	$100.89	4.386%	$105.315	$105.32	$105.30	$105.30
Purchase #5	$162.60	4.587%	$170.0585	$170.06	$170.05	$170.10
Purchase #6	$92.31	11.505%	$102.9303	$102.93	$102.95	$102.90
Purchase #7	$10.31	6.469%	$10.977	$10.98	$11.00	$11.00
7 purchase totals =	$907.44		$976.3621	$976.36	$976.35	$976.40