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	$90.88	8.516%	$98.6193	$98.62	$98.60	$98.60
Purchase #2	$236.25	6.198%	$250.8928	$250.89	$250.90	$250.90
Purchase #3	$179.60	9.114%	$195.9687	$195.97	$195.95	$196.00
Purchase #4	$96.97	3.569%	$100.4309	$100.43	$100.45	$100.40
Purchase #5	$207.89	8.650%	$225.8725	$225.87	$225.85	$225.90
Purchase #6	$91.86	4.687%	$96.1655	$96.17	$96.15	$96.20
Purchase #7	$233.43	6.708%	$249.0885	$249.09	$249.10	$249.10
7 purchase totals =	$1,136.88		$1,217.0382	$1,217.04	$1,217.00	$1,217.10