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	$33.93	12.531%	$38.1818	$38.18	$38.20	$38.20
Purchase #2	$40.31	4.699%	$42.2042	$42.20	$42.20	$42.20
Purchase #3	$116.79	9.171%	$127.5008	$127.50	$127.50	$127.50
Purchase #4	$74.75	6.254%	$79.4249	$79.42	$79.40	$79.40
Purchase #5	$180.54	3.306%	$186.5087	$186.51	$186.50	$186.50
Purchase #6	$178.53	7.806%	$192.4661	$192.47	$192.45	$192.50
Purchase #7	$41.92	9.548%	$45.9225	$45.92	$45.90	$45.90
7 purchase totals =	$666.77		$712.2090	$712.20	$712.15	$712.20