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	$127.66	11.586%	$142.4507	$142.45	$142.45	$142.50
Purchase #2	$209.25	3.517%	$216.6093	$216.61	$216.60	$216.60
Purchase #3	$134.57	10.314%	$148.4495	$148.45	$148.45	$148.40
Purchase #4	$50.34	5.628%	$53.1731	$53.17	$53.15	$53.20
Purchase #5	$100.37	11.780%	$112.1936	$112.19	$112.20	$112.20
Purchase #6	$116.53	5.189%	$122.5767	$122.58	$122.60	$122.60
Purchase #7	$23.30	5.222%	$24.5167	$24.52	$24.50	$24.50
7 purchase totals =	$762.02		$819.9696	$819.97	$819.95	$820.00