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	$45.87	8.702%	$49.8616	$49.86	$49.85	$49.90
Purchase #2	$110.38	10.773%	$122.2712	$122.27	$122.25	$122.30
Purchase #3	$216.25	10.218%	$238.3464	$238.35	$238.35	$238.30
Purchase #4	$40.74	4.573%	$42.603	$42.60	$42.60	$42.60
Purchase #5	$5.92	8.239%	$6.4077	$6.41	$6.40	$6.40
Purchase #6	$212.61	4.334%	$221.8245	$221.82	$221.80	$221.80
Purchase #7	$87.58	3.389%	$90.5481	$90.55	$90.55	$90.50
7 purchase totals =	$719.35		$771.8625	$771.86	$771.80	$771.80