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	$144.49	11.160%	$160.6151	$160.62	$160.60	$160.60
Purchase #2	$90.63	10.833%	$100.4479	$100.45	$100.45	$100.40
Purchase #3	$205.46	12.215%	$230.5569	$230.56	$230.55	$230.60
Purchase #4	$109.63	4.702%	$114.7848	$114.78	$114.80	$114.80
Purchase #5	$19.69	3.216%	$20.3232	$20.32	$20.30	$20.30
Purchase #6	$209.59	8.583%	$227.5791	$227.58	$227.60	$227.60
Purchase #7	$216.59	7.493%	$232.8191	$232.82	$232.80	$232.80
7 purchase totals =	$996.08		$1,087.1261	$1,087.13	$1,087.10	$1,087.10