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	$108.76	11.727%	$121.5143	$121.51	$121.50	$121.50
Purchase #2	$34.59	4.859%	$36.2707	$36.27	$36.25	$36.30
Purchase #3	$39.78	7.369%	$42.7114	$42.71	$42.70	$42.70
Purchase #4	$163.60	6.280%	$173.8741	$173.87	$173.85	$173.90
Purchase #5	$82.95	8.797%	$90.2471	$90.25	$90.25	$90.20
Purchase #6	$154.42	3.853%	$160.3698	$160.37	$160.35	$160.40
Purchase #7	$132.87	7.867%	$143.3229	$143.32	$143.30	$143.30
7 purchase totals =	$716.97		$768.3103	$768.30	$768.20	$768.30