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	$109.37	6.198%	$116.1488	$116.15	$116.15	$116.10
Purchase #2	$120.50	5.863%	$127.5649	$127.56	$127.55	$127.60
Purchase #3	$238.89	4.735%	$250.2014	$250.20	$250.20	$250.20
Purchase #4	$81.90	13.140%	$92.6617	$92.66	$92.65	$92.70
Purchase #5	$210.58	13.288%	$238.5619	$238.56	$238.55	$238.60
Purchase #6	$44.77	10.756%	$49.5855	$49.59	$49.60	$49.60
Purchase #7	$35.37	6.264%	$37.5856	$37.59	$37.60	$37.60
7 purchase totals =	$841.38		$912.3098	$912.31	$912.30	$912.40