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	$60.71	8.157%	$65.6621	$65.66	$65.65	$65.70
Purchase #2	$212.33	8.480%	$230.3356	$230.34	$230.35	$230.30
Purchase #3	$140.93	11.198%	$156.7113	$156.71	$156.70	$156.70
Purchase #4	$16.59	10.480%	$18.3286	$18.33	$18.35	$18.30
Purchase #5	$170.69	5.676%	$180.3784	$180.38	$180.40	$180.40
Purchase #6	$55.43	7.253%	$59.4503	$59.45	$59.45	$59.50
Purchase #7	$6.89	11.715%	$7.6972	$7.70	$7.70	$7.70
7 purchase totals =	$663.57		$718.5635	$718.57	$718.60	$718.60