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	$99.72	8.638%	$108.3338	$108.33	$108.35	$108.30
Purchase #2	$132.89	10.274%	$146.5431	$146.54	$146.55	$146.50
Purchase #3	$231.52	7.358%	$248.5552	$248.56	$248.55	$248.60
Purchase #4	$66.75	8.503%	$72.4258	$72.43	$72.45	$72.40
Purchase #5	$80.52	8.847%	$87.6436	$87.64	$87.65	$87.60
Purchase #6	$227.83	6.406%	$242.4248	$242.42	$242.40	$242.40
Purchase #7	$163.73	3.603%	$169.6292	$169.63	$169.65	$169.60
7 purchase totals =	$1,002.96		$1,075.5555	$1,075.55	$1,075.60	$1,075.40