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	$111.53	9.184%	$121.7729	$121.77	$121.75	$121.80
Purchase #2	$121.95	4.349%	$127.2536	$127.25	$127.25	$127.30
Purchase #3	$55.92	11.426%	$62.3094	$62.31	$62.30	$62.30
Purchase #4	$36.97	6.390%	$39.3324	$39.33	$39.35	$39.30
Purchase #5	$172.78	13.758%	$196.5511	$196.55	$196.55	$196.60
Purchase #6	$59.57	7.773%	$64.2004	$64.20	$64.20	$64.20
Purchase #7	$131.39	5.189%	$138.2078	$138.21	$138.20	$138.20
7 purchase totals =	$690.11		$749.6276	$749.62	$749.60	$749.70