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	$43.74	12.627%	$49.263	$49.26	$49.25	$49.30
Purchase #2	$42.59	9.547%	$46.6561	$46.66	$46.65	$46.70
Purchase #3	$39.74	11.180%	$44.1829	$44.18	$44.20	$44.20
Purchase #4	$48.65	10.771%	$53.8901	$53.89	$53.90	$53.90
Purchase #5	$241.88	13.117%	$273.6074	$273.61	$273.60	$273.60
Purchase #6	$49.31	11.308%	$54.886	$54.89	$54.90	$54.90
Purchase #7	$105.79	8.641%	$114.9313	$114.93	$114.95	$114.90
7 purchase totals =	$571.70		$637.4168	$637.42	$637.45	$637.50