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	$55.82	10.188%	$61.5069	$61.51	$61.50	$61.50
Purchase #2	$118.85	11.401%	$132.4001	$132.40	$132.40	$132.40
Purchase #3	$61.41	9.752%	$67.3987	$67.40	$67.40	$67.40
Purchase #4	$220.25	12.247%	$247.224	$247.22	$247.20	$247.20
Purchase #5	$123.28	3.766%	$127.9227	$127.92	$127.90	$127.90
Purchase #6	$118.36	9.116%	$129.1497	$129.15	$129.15	$129.10
Purchase #7	$41.61	10.430%	$45.9499	$45.95	$45.95	$45.90
7 purchase totals =	$739.58		$811.5520	$811.55	$811.50	$811.40