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	$137.72	5.370%	$145.1156	$145.12	$145.10	$145.10
Purchase #2	$167.93	11.633%	$187.4653	$187.47	$187.45	$187.50
Purchase #3	$40.90	4.395%	$42.6976	$42.70	$42.70	$42.70
Purchase #4	$138.79	12.722%	$156.4469	$156.45	$156.45	$156.40
Purchase #5	$43.25	3.106%	$44.5933	$44.59	$44.60	$44.60
Purchase #6	$106.36	12.294%	$119.4359	$119.44	$119.45	$119.40
Purchase #7	$223.87	6.454%	$238.3186	$238.32	$238.30	$238.30
7 purchase totals =	$858.82		$934.0732	$934.09	$934.05	$934.00