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	$83.87	3.249%	$86.5949	$86.59	$86.60	$86.60
Purchase #2	$146.63	10.654%	$162.252	$162.25	$162.25	$162.30
Purchase #3	$52.46	4.505%	$54.8233	$54.82	$54.80	$54.80
Purchase #4	$115.27	10.688%	$127.5901	$127.59	$127.60	$127.60
Purchase #5	$116.37	8.650%	$126.436	$126.44	$126.45	$126.40
Purchase #6	$115.25	6.865%	$123.1619	$123.16	$123.15	$123.20
Purchase #7	$126.98	11.794%	$141.956	$141.96	$141.95	$142.00
7 purchase totals =	$756.83		$822.8142	$822.81	$822.80	$822.90