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	$61.93	5.305%	$65.2154	$65.22	$65.20	$65.20
Purchase #2	$22.89	6.659%	$24.4142	$24.41	$24.40	$24.40
Purchase #3	$73.70	9.743%	$80.8806	$80.88	$80.90	$80.90
Purchase #4	$213.78	12.665%	$240.8552	$240.86	$240.85	$240.90
Purchase #5	$43.68	11.278%	$48.6062	$48.61	$48.60	$48.60
Purchase #6	$109.83	9.571%	$120.3418	$120.34	$120.35	$120.30
Purchase #7	$164.26	12.777%	$185.2475	$185.25	$185.25	$185.20
7 purchase totals =	$690.07		$765.5609	$765.57	$765.55	$765.50