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	$126.50	11.363%	$140.8742	$140.87	$140.85	$140.90
Purchase #2	$33.47	13.416%	$37.9603	$37.96	$37.95	$38.00
Purchase #3	$231.97	10.103%	$255.4059	$255.41	$255.40	$255.40
Purchase #4	$83.30	11.441%	$92.8304	$92.83	$92.85	$92.80
Purchase #5	$123.39	8.364%	$133.7103	$133.71	$133.70	$133.70
Purchase #6	$41.98	9.164%	$45.827	$45.83	$45.85	$45.80
Purchase #7	$138.68	10.327%	$153.0015	$153.00	$153.00	$153.00
7 purchase totals =	$779.29		$859.6096	$859.61	$859.60	$859.60