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	$121.93	4.330%	$127.2096	$127.21	$127.20	$127.20
Purchase #2	$236.85	10.500%	$261.7193	$261.72	$261.70	$261.70
Purchase #3	$232.98	8.327%	$252.3802	$252.38	$252.40	$252.40
Purchase #4	$63.28	6.773%	$67.566	$67.57	$67.55	$67.60
Purchase #5	$215.68	10.420%	$238.1539	$238.15	$238.15	$238.20
Purchase #6	$45.50	10.649%	$50.3453	$50.35	$50.35	$50.30
Purchase #7	$187.27	6.200%	$198.8807	$198.88	$198.90	$198.90
7 purchase totals =	$1,103.49		$1,196.2550	$1,196.26	$1,196.25	$1,196.30