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	$229.51	3.634%	$237.8504	$237.85	$237.85	$237.90
Purchase #2	$152.94	11.615%	$170.704	$170.70	$170.70	$170.70
Purchase #3	$147.51	5.481%	$155.595	$155.60	$155.60	$155.60
Purchase #4	$116.83	8.447%	$126.6986	$126.70	$126.70	$126.70
Purchase #5	$157.90	9.183%	$172.4	$172.40	$172.40	$172.40
Purchase #6	$27.58	12.729%	$31.0907	$31.09	$31.10	$31.10
Purchase #7	$104.47	4.839%	$109.5253	$109.53	$109.55	$109.50
7 purchase totals =	$936.74		$1,003.8640	$1,003.87	$1,003.90	$1,003.90