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	$26.55	11.247%	$29.5361	$29.54	$29.55	$29.50
Purchase #2	$44.29	4.187%	$46.1444	$46.14	$46.15	$46.10
Purchase #3	$181.56	13.414%	$205.9145	$205.91	$205.90	$205.90
Purchase #4	$133.66	3.830%	$138.7792	$138.78	$138.80	$138.80
Purchase #5	$213.60	4.825%	$223.9062	$223.91	$223.90	$223.90
Purchase #6	$121.98	4.421%	$127.3727	$127.37	$127.35	$127.40
Purchase #7	$33.26	13.655%	$37.8017	$37.80	$37.80	$37.80
7 purchase totals =	$754.90		$809.4548	$809.45	$809.45	$809.40