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	$145.46	8.874%	$158.3681	$158.37	$158.35	$158.40
Purchase #2	$181.75	8.160%	$196.5808	$196.58	$196.60	$196.60
Purchase #3	$90.75	9.652%	$99.5092	$99.51	$99.50	$99.50
Purchase #4	$131.86	3.795%	$136.8641	$136.86	$136.85	$136.90
Purchase #5	$209.64	3.577%	$217.1388	$217.14	$217.15	$217.10
Purchase #6	$180.79	13.135%	$204.5368	$204.54	$204.55	$204.50
Purchase #7	$220.56	11.848%	$246.6919	$246.69	$246.70	$246.70
7 purchase totals =	$1,160.81		$1,259.6897	$1,259.69	$1,259.70	$1,259.70