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	$35.47	7.670%	$38.1905	$38.19	$38.20	$38.20
Purchase #2	$47.73	9.426%	$52.229	$52.23	$52.25	$52.20
Purchase #3	$214.73	3.109%	$221.406	$221.41	$221.40	$221.40
Purchase #4	$25.47	8.198%	$27.558	$27.56	$27.55	$27.60
Purchase #5	$47.47	3.553%	$49.1566	$49.16	$49.15	$49.20
Purchase #6	$207.53	9.828%	$227.926	$227.93	$227.95	$227.90
Purchase #7	$45.65	12.307%	$51.2681	$51.27	$51.25	$51.30
7 purchase totals =	$624.05		$667.7342	$667.75	$667.75	$667.80