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	$123.90	10.155%	$136.482	$136.48	$136.50	$136.50
Purchase #2	$90.59	4.710%	$94.8568	$94.86	$94.85	$94.90
Purchase #3	$28.55	3.857%	$29.6512	$29.65	$29.65	$29.70
Purchase #4	$72.29	8.859%	$78.6942	$78.69	$78.70	$78.70
Purchase #5	$231.67	4.337%	$241.7175	$241.72	$241.70	$241.70
Purchase #6	$111.27	13.859%	$126.6909	$126.69	$126.70	$126.70
Purchase #7	$50.26	5.516%	$53.0323	$53.03	$53.05	$53.00
7 purchase totals =	$708.53		$761.1249	$761.12	$761.15	$761.20