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	$78.70	13.724%	$89.5008	$89.50	$89.50	$89.50
Purchase #2	$60.97	3.120%	$62.8723	$62.87	$62.85	$62.90
Purchase #3	$248.65	12.258%	$279.1295	$279.13	$279.15	$279.10
Purchase #4	$229.62	10.436%	$253.5831	$253.58	$253.60	$253.60
Purchase #5	$76.86	8.628%	$83.4915	$83.49	$83.50	$83.50
Purchase #6	$173.67	7.256%	$186.2715	$186.27	$186.25	$186.30
Purchase #7	$121.58	12.475%	$136.7471	$136.75	$136.75	$136.70
7 purchase totals =	$990.05		$1,091.5958	$1,091.59	$1,091.60	$1,091.60