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	$50.57	12.749%	$57.0172	$57.02	$57.00	$57.00
Purchase #2	$128.70	12.246%	$144.4606	$144.46	$144.45	$144.50
Purchase #3	$196.70	3.410%	$203.4075	$203.41	$203.40	$203.40
Purchase #4	$35.60	8.204%	$38.5206	$38.52	$38.50	$38.50
Purchase #5	$94.73	5.193%	$99.6493	$99.65	$99.65	$99.60
Purchase #6	$208.96	6.392%	$222.3167	$222.32	$222.30	$222.30
Purchase #7	$71.95	12.669%	$81.0653	$81.07	$81.05	$81.10
7 purchase totals =	$787.21		$846.4372	$846.45	$846.35	$846.40