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	$11.90	7.853%	$12.8345	$12.83	$12.85	$12.80
Purchase #2	$57.52	6.528%	$61.2749	$61.27	$61.25	$61.30
Purchase #3	$182.49	12.588%	$205.4618	$205.46	$205.45	$205.50
Purchase #4	$166.94	7.662%	$179.7309	$179.73	$179.75	$179.70
Purchase #5	$52.25	12.299%	$58.6762	$58.68	$58.70	$58.70
Purchase #6	$166.79	11.746%	$186.3812	$186.38	$186.40	$186.40
Purchase #7	$91.74	9.550%	$100.5012	$100.50	$100.50	$100.50
7 purchase totals =	$729.63		$804.8607	$804.85	$804.90	$804.90