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	$127.66	3.854%	$132.58	$132.58	$132.60	$132.60
Purchase #2	$85.56	5.227%	$90.0322	$90.03	$90.05	$90.00
Purchase #3	$53.58	3.514%	$55.4628	$55.46	$55.45	$55.50
Purchase #4	$54.40	8.173%	$58.8461	$58.85	$58.85	$58.80
Purchase #5	$119.27	4.525%	$124.667	$124.67	$124.65	$124.70
Purchase #6	$119.91	6.594%	$127.8169	$127.82	$127.80	$127.80
Purchase #7	$182.30	4.719%	$190.9027	$190.90	$190.90	$190.90
7 purchase totals =	$742.68		$780.3077	$780.31	$780.30	$780.30