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	$188.44	13.170%	$213.2575	$213.26	$213.25	$213.30
Purchase #2	$164.80	5.291%	$173.5196	$173.52	$173.50	$173.50
Purchase #3	$95.73	10.154%	$105.4504	$105.45	$105.45	$105.50
Purchase #4	$125.47	11.181%	$139.4988	$139.50	$139.50	$139.50
Purchase #5	$69.37	13.593%	$78.7995	$78.80	$78.80	$78.80
Purchase #6	$100.36	10.816%	$111.2149	$111.21	$111.20	$111.20
Purchase #7	$5.45	7.186%	$5.8416	$5.84	$5.85	$5.80
7 purchase totals =	$749.62		$827.5823	$827.58	$827.55	$827.60