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	$37.94	6.178%	$40.2839	$40.28	$40.30	$40.30
Purchase #2	$222.42	3.391%	$229.9623	$229.96	$229.95	$230.00
Purchase #3	$35.38	9.129%	$38.6098	$38.61	$38.60	$38.60
Purchase #4	$92.86	4.479%	$97.0192	$97.02	$97.00	$97.00
Purchase #5	$172.26	7.579%	$185.3156	$185.32	$185.30	$185.30
Purchase #6	$12.91	5.429%	$13.6109	$13.61	$13.60	$13.60
Purchase #7	$51.76	11.261%	$57.5887	$57.59	$57.60	$57.60
7 purchase totals =	$625.53		$662.3904	$662.39	$662.35	$662.40