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	$11.78	9.393%	$12.8865	$12.89	$12.90	$12.90
Purchase #2	$133.40	7.403%	$143.2756	$143.28	$143.30	$143.30
Purchase #3	$162.95	4.604%	$170.4522	$170.45	$170.45	$170.50
Purchase #4	$133.68	13.484%	$151.7054	$151.71	$151.70	$151.70
Purchase #5	$50.66	9.591%	$55.5188	$55.52	$55.50	$55.50
Purchase #6	$213.44	9.782%	$234.3187	$234.32	$234.30	$234.30
Purchase #7	$213.87	11.457%	$238.3731	$238.37	$238.35	$238.40
7 purchase totals =	$919.78		$1,006.5303	$1,006.54	$1,006.50	$1,006.60