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	$197.99	3.640%	$205.1968	$205.20	$205.20	$205.20
Purchase #2	$112.27	13.276%	$127.175	$127.18	$127.20	$127.20
Purchase #3	$52.90	5.477%	$55.7973	$55.80	$55.80	$55.80
Purchase #4	$50.32	12.300%	$56.5094	$56.51	$56.50	$56.50
Purchase #5	$134.87	7.773%	$145.3534	$145.35	$145.35	$145.40
Purchase #6	$164.90	9.374%	$180.3577	$180.36	$180.35	$180.40
Purchase #7	$188.57	10.208%	$207.8192	$207.82	$207.80	$207.80
7 purchase totals =	$901.82		$978.2088	$978.22	$978.20	$978.30