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	$229.85	9.122%	$250.8169	$250.82	$250.80	$250.80
Purchase #2	$35.89	11.518%	$40.0238	$40.02	$40.00	$40.00
Purchase #3	$227.73	10.456%	$251.5414	$251.54	$251.55	$251.50
Purchase #4	$227.75	5.351%	$239.9369	$239.94	$239.95	$239.90
Purchase #5	$48.30	13.136%	$54.6447	$54.64	$54.65	$54.60
Purchase #6	$191.64	10.808%	$212.3525	$212.35	$212.35	$212.40
Purchase #7	$138.92	5.788%	$146.9607	$146.96	$146.95	$147.00
7 purchase totals =	$1,100.08		$1,196.2769	$1,196.27	$1,196.25	$1,196.20