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	$99.50	6.327%	$105.7954	$105.80	$105.80	$105.80
Purchase #2	$78.42	3.796%	$81.3968	$81.40	$81.40	$81.40
Purchase #3	$229.27	8.701%	$249.2188	$249.22	$249.20	$249.20
Purchase #4	$109.41	3.129%	$112.8334	$112.83	$112.85	$112.80
Purchase #5	$57.82	6.423%	$61.5338	$61.53	$61.55	$61.50
Purchase #6	$99.82	13.493%	$113.2887	$113.29	$113.30	$113.30
Purchase #7	$12.92	5.376%	$13.6146	$13.61	$13.60	$13.60
7 purchase totals =	$687.16		$737.6815	$737.68	$737.70	$737.60