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	$16.45	8.824%	$17.9015	$17.90	$17.90	$17.90
Purchase #2	$132.48	9.269%	$144.7596	$144.76	$144.75	$144.80
Purchase #3	$131.75	7.530%	$141.6708	$141.67	$141.65	$141.70
Purchase #4	$94.27	11.808%	$105.4014	$105.40	$105.40	$105.40
Purchase #5	$30.88	7.596%	$33.2256	$33.23	$33.25	$33.20
Purchase #6	$162.38	5.163%	$170.7637	$170.76	$170.75	$170.80
Purchase #7	$90.39	11.626%	$100.8987	$100.90	$100.90	$100.90
7 purchase totals =	$658.60		$714.6213	$714.62	$714.60	$714.70