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	$22.93	10.776%	$25.4009	$25.40	$25.40	$25.40
Purchase #2	$116.52	13.313%	$132.0323	$132.03	$132.05	$132.00
Purchase #3	$239.38	6.790%	$255.6339	$255.63	$255.65	$255.60
Purchase #4	$88.67	11.674%	$99.0213	$99.02	$99.00	$99.00
Purchase #5	$100.94	4.657%	$105.6408	$105.64	$105.65	$105.60
Purchase #6	$83.68	8.629%	$90.9007	$90.90	$90.90	$90.90
Purchase #7	$101.62	9.688%	$111.4649	$111.46	$111.45	$111.50
7 purchase totals =	$753.74		$820.0948	$820.08	$820.10	$820.00