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	$17.56	10.831%	$19.4619	$19.46	$19.45	$19.50
Purchase #2	$201.90	12.855%	$227.8542	$227.85	$227.85	$227.90
Purchase #3	$190.27	11.131%	$211.449	$211.45	$211.45	$211.40
Purchase #4	$22.42	3.811%	$23.2744	$23.27	$23.25	$23.30
Purchase #5	$196.87	4.482%	$205.6937	$205.69	$205.70	$205.70
Purchase #6	$189.39	10.138%	$208.5904	$208.59	$208.60	$208.60
Purchase #7	$29.45	8.700%	$32.0122	$32.01	$32.00	$32.00
7 purchase totals =	$847.86		$928.3358	$928.32	$928.30	$928.40