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	$113.88	12.683%	$128.3234	$128.32	$128.30	$128.30
Purchase #2	$144.85	9.389%	$158.45	$158.45	$158.45	$158.50
Purchase #3	$67.29	8.360%	$72.9154	$72.92	$72.90	$72.90
Purchase #4	$230.98	5.819%	$244.4207	$244.42	$244.40	$244.40
Purchase #5	$158.72	10.387%	$175.2062	$175.21	$175.20	$175.20
Purchase #6	$152.27	7.448%	$163.6111	$163.61	$163.60	$163.60
Purchase #7	$199.72	11.157%	$222.0028	$222.00	$222.00	$222.00
7 purchase totals =	$1,067.71		$1,164.9296	$1,164.93	$1,164.85	$1,164.90