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	$36.36	13.651%	$41.3235	$41.32	$41.30	$41.30
Purchase #2	$94.38	11.444%	$105.1808	$105.18	$105.20	$105.20
Purchase #3	$161.45	13.441%	$183.1505	$183.15	$183.15	$183.20
Purchase #4	$216.34	11.636%	$241.5133	$241.51	$241.50	$241.50
Purchase #5	$98.45	12.453%	$110.71	$110.71	$110.70	$110.70
Purchase #6	$160.83	11.680%	$179.6149	$179.61	$179.60	$179.60
Purchase #7	$117.28	8.323%	$127.0412	$127.04	$127.05	$127.00
7 purchase totals =	$885.09		$988.5342	$988.52	$988.50	$988.50