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	$111.88	6.283%	$118.9094	$118.91	$118.90	$118.90
Purchase #2	$47.59	9.757%	$52.2334	$52.23	$52.25	$52.20
Purchase #3	$49.54	13.557%	$56.2561	$56.26	$56.25	$56.30
Purchase #4	$230.72	7.254%	$247.4564	$247.46	$247.45	$247.50
Purchase #5	$182.95	5.169%	$192.4067	$192.41	$192.40	$192.40
Purchase #6	$120.46	6.168%	$127.89	$127.89	$127.90	$127.90
Purchase #7	$241.65	11.758%	$270.0632	$270.06	$270.05	$270.10
7 purchase totals =	$984.79		$1,065.2152	$1,065.22	$1,065.20	$1,065.30