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	$63.46	6.151%	$67.3634	$67.36	$67.35	$67.40
Purchase #2	$161.32	12.643%	$181.7157	$181.72	$181.70	$181.70
Purchase #3	$113.36	12.584%	$127.6252	$127.63	$127.65	$127.60
Purchase #4	$43.27	11.286%	$48.1535	$48.15	$48.15	$48.20
Purchase #5	$30.68	8.375%	$33.2495	$33.25	$33.25	$33.20
Purchase #6	$227.59	4.709%	$238.3072	$238.31	$238.30	$238.30
Purchase #7	$104.91	4.104%	$109.2155	$109.22	$109.20	$109.20
7 purchase totals =	$744.59		$805.6300	$805.64	$805.60	$805.60