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	$91.34	10.471%	$100.9042	$100.90	$100.90	$100.90
Purchase #2	$48.27	3.536%	$49.9768	$49.98	$50.00	$50.00
Purchase #3	$128.47	11.534%	$143.2877	$143.29	$143.30	$143.30
Purchase #4	$162.90	4.693%	$170.5449	$170.54	$170.55	$170.50
Purchase #5	$125.25	7.361%	$134.4697	$134.47	$134.45	$134.50
Purchase #6	$52.26	10.501%	$57.7478	$57.75	$57.75	$57.70
Purchase #7	$95.50	6.780%	$101.9749	$101.97	$101.95	$102.00
7 purchase totals =	$703.99		$758.9060	$758.90	$758.90	$758.90