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	$230.70	12.159%	$258.7508	$258.75	$258.75	$258.80
Purchase #2	$130.53	4.413%	$136.2903	$136.29	$136.30	$136.30
Purchase #3	$75.53	9.140%	$82.4334	$82.43	$82.45	$82.40
Purchase #4	$192.75	13.254%	$218.2971	$218.30	$218.30	$218.30
Purchase #5	$163.31	13.265%	$184.9731	$184.97	$184.95	$185.00
Purchase #6	$117.38	8.136%	$126.93	$126.93	$126.95	$126.90
Purchase #7	$79.67	13.721%	$90.6015	$90.60	$90.60	$90.60
7 purchase totals =	$989.87		$1,098.2762	$1,098.27	$1,098.30	$1,098.30