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	$176.44	6.707%	$188.2738	$188.27	$188.25	$188.30
Purchase #2	$113.85	12.834%	$128.4615	$128.46	$128.45	$128.50
Purchase #3	$231.25	8.819%	$251.6439	$251.64	$251.65	$251.60
Purchase #4	$250.97	4.535%	$262.3515	$262.35	$262.35	$262.40
Purchase #5	$173.32	9.607%	$189.9709	$189.97	$189.95	$190.00
Purchase #6	$242.31	5.604%	$255.8891	$255.89	$255.90	$255.90
Purchase #7	$55.71	11.176%	$61.9361	$61.94	$61.95	$61.90
7 purchase totals =	$1,243.85		$1,338.5268	$1,338.52	$1,338.50	$1,338.60