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	$118.31	7.847%	$127.5938	$127.59	$127.60	$127.60
Purchase #2	$46.92	13.366%	$53.1913	$53.19	$53.20	$53.20
Purchase #3	$218.52	3.325%	$225.7858	$225.79	$225.80	$225.80
Purchase #4	$118.84	12.602%	$133.8162	$133.82	$133.80	$133.80
Purchase #5	$152.43	11.115%	$169.3726	$169.37	$169.35	$169.40
Purchase #6	$62.33	10.610%	$68.9432	$68.94	$68.95	$68.90
Purchase #7	$126.79	6.312%	$134.793	$134.79	$134.80	$134.80
7 purchase totals =	$844.14		$913.4959	$913.49	$913.50	$913.50