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	$75.35	7.327%	$80.8709	$80.87	$80.85	$80.90
Purchase #2	$113.56	4.713%	$118.9121	$118.91	$118.90	$118.90
Purchase #3	$163.28	6.373%	$173.6858	$173.69	$173.70	$173.70
Purchase #4	$95.30	10.676%	$105.4742	$105.47	$105.45	$105.50
Purchase #5	$22.59	3.824%	$23.4538	$23.45	$23.45	$23.50
Purchase #6	$51.33	3.219%	$52.9823	$52.98	$53.00	$53.00
Purchase #7	$196.52	13.464%	$222.9795	$222.98	$223.00	$223.00
7 purchase totals =	$717.93		$778.3586	$778.35	$778.35	$778.50