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	$113.42	12.781%	$127.9162	$127.92	$127.90	$127.90
Purchase #2	$137.29	6.634%	$146.3978	$146.40	$146.40	$146.40
Purchase #3	$41.64	10.317%	$45.936	$45.94	$45.95	$45.90
Purchase #4	$63.86	9.662%	$70.0302	$70.03	$70.05	$70.00
Purchase #5	$10.57	9.669%	$11.592	$11.59	$11.60	$11.60
Purchase #6	$112.89	4.683%	$118.1766	$118.18	$118.20	$118.20
Purchase #7	$45.84	10.439%	$50.6252	$50.63	$50.65	$50.60
7 purchase totals =	$525.51		$570.6740	$570.69	$570.75	$570.60