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	$23.91	4.152%	$24.9027	$24.90	$24.90	$24.90
Purchase #2	$39.54	7.598%	$42.5442	$42.54	$42.55	$42.50
Purchase #3	$166.72	12.742%	$187.9635	$187.96	$187.95	$188.00
Purchase #4	$113.44	5.118%	$119.2459	$119.25	$119.25	$119.20
Purchase #5	$38.86	13.382%	$44.0602	$44.06	$44.05	$44.10
Purchase #6	$122.25	4.142%	$127.3136	$127.31	$127.30	$127.30
Purchase #7	$62.76	8.500%	$68.0946	$68.09	$68.10	$68.10
7 purchase totals =	$567.48		$614.1247	$614.11	$614.10	$614.10