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	$11.97	4.737%	$12.537	$12.54	$12.55	$12.50
Purchase #2	$36.87	6.824%	$39.386	$39.39	$39.40	$39.40
Purchase #3	$179.66	4.264%	$187.3207	$187.32	$187.30	$187.30
Purchase #4	$65.55	10.860%	$72.6687	$72.67	$72.65	$72.70
Purchase #5	$7.29	6.546%	$7.7672	$7.77	$7.75	$7.80
Purchase #6	$211.49	5.305%	$222.7095	$222.71	$222.70	$222.70
Purchase #7	$196.93	4.408%	$205.6107	$205.61	$205.60	$205.60
7 purchase totals =	$709.76		$747.9998	$748.01	$747.95	$748.00