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	$84.50	13.492%	$95.9007	$95.90	$95.90	$95.90
Purchase #2	$99.32	8.147%	$107.4116	$107.41	$107.40	$107.40
Purchase #3	$156.45	7.344%	$167.9397	$167.94	$167.95	$167.90
Purchase #4	$112.55	13.849%	$128.137	$128.14	$128.15	$128.10
Purchase #5	$84.41	6.772%	$90.1262	$90.13	$90.15	$90.10
Purchase #6	$172.56	4.630%	$180.5495	$180.55	$180.55	$180.50
Purchase #7	$128.68	13.293%	$145.7854	$145.79	$145.80	$145.80
7 purchase totals =	$838.47		$915.8501	$915.86	$915.90	$915.70