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	$135.37	6.486%	$144.1501	$144.15	$144.15	$144.20
Purchase #2	$15.73	4.847%	$16.4924	$16.49	$16.50	$16.50
Purchase #3	$145.94	13.365%	$165.4449	$165.44	$165.45	$165.40
Purchase #4	$128.38	13.789%	$146.0823	$146.08	$146.10	$146.10
Purchase #5	$108.59	9.131%	$118.5054	$118.51	$118.50	$118.50
Purchase #6	$36.65	5.443%	$38.6449	$38.64	$38.65	$38.60
Purchase #7	$42.81	5.397%	$45.1205	$45.12	$45.10	$45.10
7 purchase totals =	$613.47		$674.4405	$674.43	$674.45	$674.40