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	$173.30	13.315%	$196.3749	$196.37	$196.35	$196.40
Purchase #2	$144.59	8.434%	$156.7847	$156.78	$156.80	$156.80
Purchase #3	$67.87	6.497%	$72.2795	$72.28	$72.30	$72.30
Purchase #4	$27.45	6.795%	$29.3152	$29.32	$29.30	$29.30
Purchase #5	$184.92	11.196%	$205.6236	$205.62	$205.60	$205.60
Purchase #6	$160.58	10.789%	$177.905	$177.91	$177.90	$177.90
Purchase #7	$98.85	9.520%	$108.2605	$108.26	$108.25	$108.30
7 purchase totals =	$857.56		$946.5434	$946.54	$946.50	$946.60