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	$89.79	5.181%	$94.442	$94.44	$94.45	$94.40
Purchase #2	$98.86	3.427%	$102.2479	$102.25	$102.25	$102.20
Purchase #3	$24.43	11.184%	$27.1623	$27.16	$27.15	$27.20
Purchase #4	$110.69	5.340%	$116.6008	$116.60	$116.60	$116.60
Purchase #5	$200.42	10.684%	$221.8329	$221.83	$221.85	$221.80
Purchase #6	$98.49	3.440%	$101.8781	$101.88	$101.90	$101.90
Purchase #7	$126.35	8.824%	$137.4991	$137.50	$137.50	$137.50
7 purchase totals =	$749.03		$801.6631	$801.66	$801.70	$801.60