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	$242.89	11.697%	$271.3008	$271.30	$271.30	$271.30
Purchase #2	$127.27	11.703%	$142.1644	$142.16	$142.15	$142.20
Purchase #3	$208.35	9.252%	$227.6265	$227.63	$227.65	$227.60
Purchase #4	$223.40	4.559%	$233.5848	$233.58	$233.60	$233.60
Purchase #5	$177.47	12.816%	$200.2146	$200.21	$200.20	$200.20
Purchase #6	$217.50	12.576%	$244.8528	$244.85	$244.85	$244.90
Purchase #7	$172.30	9.734%	$189.0717	$189.07	$189.05	$189.10
7 purchase totals =	$1,369.18		$1,508.8156	$1,508.80	$1,508.80	$1,508.90