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	$109.85	3.409%	$113.5948	$113.59	$113.60	$113.60
Purchase #2	$50.37	5.581%	$53.1811	$53.18	$53.20	$53.20
Purchase #3	$130.89	12.204%	$146.8638	$146.86	$146.85	$146.90
Purchase #4	$151.58	13.571%	$172.1509	$172.15	$172.15	$172.20
Purchase #5	$130.94	6.336%	$139.2364	$139.24	$139.25	$139.20
Purchase #6	$58.43	12.553%	$65.7647	$65.76	$65.75	$65.80
Purchase #7	$162.58	13.798%	$185.0128	$185.01	$185.00	$185.00
7 purchase totals =	$794.64		$875.8045	$875.79	$875.80	$875.90