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	$52.72	12.644%	$59.3859	$59.39	$59.40	$59.40
Purchase #2	$77.49	3.729%	$80.3796	$80.38	$80.40	$80.40
Purchase #3	$170.49	12.665%	$192.0826	$192.08	$192.10	$192.10
Purchase #4	$14.88	4.728%	$15.5835	$15.58	$15.60	$15.60
Purchase #5	$14.51	3.759%	$15.0554	$15.06	$15.05	$15.10
Purchase #6	$187.89	6.500%	$200.1029	$200.10	$200.10	$200.10
Purchase #7	$179.86	5.222%	$189.2523	$189.25	$189.25	$189.30
7 purchase totals =	$697.84		$751.8422	$751.84	$751.90	$752.00