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	$8.25	11.625%	$9.2091	$9.21	$9.20	$9.20
Purchase #2	$130.97	10.239%	$144.38	$144.38	$144.40	$144.40
Purchase #3	$113.39	13.262%	$128.4278	$128.43	$128.45	$128.40
Purchase #4	$164.74	10.296%	$181.7016	$181.70	$181.70	$181.70
Purchase #5	$93.50	7.438%	$100.4545	$100.45	$100.45	$100.50
Purchase #6	$98.97	12.671%	$111.5105	$111.51	$111.50	$111.50
Purchase #7	$216.51	4.207%	$225.6186	$225.62	$225.60	$225.60
7 purchase totals =	$826.33		$901.3021	$901.30	$901.30	$901.30