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	$155.34	11.302%	$172.8965	$172.90	$172.90	$172.90
Purchase #2	$89.72	4.583%	$93.8319	$93.83	$93.85	$93.80
Purchase #3	$229.98	12.743%	$259.2864	$259.29	$259.30	$259.30
Purchase #4	$59.72	5.280%	$62.8732	$62.87	$62.85	$62.90
Purchase #5	$55.69	8.487%	$60.4164	$60.42	$60.40	$60.40
Purchase #6	$120.43	11.772%	$134.607	$134.61	$134.60	$134.60
Purchase #7	$94.98	13.576%	$107.8745	$107.87	$107.85	$107.90
7 purchase totals =	$805.86		$891.7859	$891.79	$891.75	$891.80