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	$177.27	5.249%	$186.5749	$186.57	$186.55	$186.60
Purchase #2	$103.94	7.587%	$111.8259	$111.83	$111.85	$111.80
Purchase #3	$6.54	7.408%	$7.0245	$7.02	$7.00	$7.00
Purchase #4	$132.93	11.566%	$148.3047	$148.30	$148.30	$148.30
Purchase #5	$16.42	13.768%	$18.6807	$18.68	$18.70	$18.70
Purchase #6	$175.53	11.734%	$196.1267	$196.13	$196.15	$196.10
Purchase #7	$213.98	12.366%	$240.4408	$240.44	$240.45	$240.40
7 purchase totals =	$826.61		$908.9782	$908.97	$909.00	$908.90