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	$49.51	7.392%	$53.1698	$53.17	$53.15	$53.20
Purchase #2	$179.36	13.180%	$202.9996	$203.00	$203.00	$203.00
Purchase #3	$106.95	4.246%	$111.4911	$111.49	$111.50	$111.50
Purchase #4	$78.89	5.856%	$83.5098	$83.51	$83.50	$83.50
Purchase #5	$22.45	12.293%	$25.2098	$25.21	$25.20	$25.20
Purchase #6	$151.48	3.235%	$156.3804	$156.38	$156.40	$156.40
Purchase #7	$41.53	5.716%	$43.9039	$43.90	$43.90	$43.90
7 purchase totals =	$630.17		$676.6644	$676.66	$676.65	$676.70