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	$13.70	12.759%	$15.448	$15.45	$15.45	$15.40
Purchase #2	$136.42	3.549%	$141.2615	$141.26	$141.25	$141.30
Purchase #3	$240.85	5.763%	$254.7302	$254.73	$254.75	$254.70
Purchase #4	$153.90	8.404%	$166.8338	$166.83	$166.85	$166.80
Purchase #5	$137.73	9.339%	$150.5926	$150.59	$150.60	$150.60
Purchase #6	$40.96	5.857%	$43.359	$43.36	$43.35	$43.40
Purchase #7	$100.98	7.265%	$108.3162	$108.32	$108.30	$108.30
7 purchase totals =	$824.54		$880.5413	$880.54	$880.55	$880.50