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	$78.69	6.560%	$83.8521	$83.85	$83.85	$83.90
Purchase #2	$171.80	3.246%	$177.3766	$177.38	$177.40	$177.40
Purchase #3	$68.92	6.770%	$73.5859	$73.59	$73.60	$73.60
Purchase #4	$127.38	9.472%	$139.4454	$139.45	$139.45	$139.40
Purchase #5	$216.75	3.161%	$223.6015	$223.60	$223.60	$223.60
Purchase #6	$101.87	9.302%	$111.3459	$111.35	$111.35	$111.30
Purchase #7	$217.63	7.195%	$233.2885	$233.29	$233.30	$233.30
7 purchase totals =	$983.04		$1,042.4959	$1,042.51	$1,042.55	$1,042.50