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	$19.50	8.383%	$21.1347	$21.13	$21.15	$21.10
Purchase #2	$223.52	5.608%	$236.055	$236.06	$236.05	$236.10
Purchase #3	$126.61	13.632%	$143.8695	$143.87	$143.85	$143.90
Purchase #4	$28.56	13.667%	$32.4633	$32.46	$32.45	$32.50
Purchase #5	$56.75	4.527%	$59.3191	$59.32	$59.30	$59.30
Purchase #6	$21.67	12.676%	$24.4169	$24.42	$24.40	$24.40
Purchase #7	$234.98	11.746%	$262.5808	$262.58	$262.60	$262.60
7 purchase totals =	$711.59		$779.8393	$779.84	$779.80	$779.90