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	$96.62	6.168%	$102.5795	$102.58	$102.60	$102.60
Purchase #2	$224.33	13.105%	$253.7284	$253.73	$253.75	$253.70
Purchase #3	$161.27	11.600%	$179.9773	$179.98	$180.00	$180.00
Purchase #4	$12.79	5.607%	$13.5071	$13.51	$13.50	$13.50
Purchase #5	$217.55	11.567%	$242.714	$242.71	$242.70	$242.70
Purchase #6	$250.83	11.224%	$278.9832	$278.98	$279.00	$279.00
Purchase #7	$53.37	5.456%	$56.2819	$56.28	$56.30	$56.30
7 purchase totals =	$1,016.76		$1,127.7714	$1,127.77	$1,127.85	$1,127.80