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	$25.33	4.451%	$26.4574	$26.46	$26.45	$26.50
Purchase #2	$100.43	10.768%	$111.2443	$111.24	$111.25	$111.20
Purchase #3	$138.32	7.154%	$148.2154	$148.22	$148.20	$148.20
Purchase #4	$143.50	13.178%	$162.4104	$162.41	$162.40	$162.40
Purchase #5	$9.67	10.817%	$10.716	$10.72	$10.70	$10.70
Purchase #6	$217.62	9.546%	$238.394	$238.39	$238.40	$238.40
Purchase #7	$136.85	13.648%	$155.5273	$155.53	$155.55	$155.50
7 purchase totals =	$771.72		$852.9648	$852.97	$852.95	$852.90