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	$37.33	5.687%	$39.453	$39.45	$39.45	$39.50
Purchase #2	$98.54	7.130%	$105.5659	$105.57	$105.55	$105.60
Purchase #3	$51.36	5.384%	$54.1252	$54.13	$54.15	$54.10
Purchase #4	$34.99	13.793%	$39.8162	$39.82	$39.80	$39.80
Purchase #5	$125.66	12.116%	$140.885	$140.89	$140.90	$140.90
Purchase #6	$166.32	4.366%	$173.5815	$173.58	$173.60	$173.60
Purchase #7	$168.94	4.314%	$176.2281	$176.23	$176.25	$176.20
7 purchase totals =	$683.14		$729.6549	$729.67	$729.70	$729.70