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	$132.37	13.156%	$149.7846	$149.78	$149.80	$149.80
Purchase #2	$240.50	12.789%	$271.2575	$271.26	$271.25	$271.30
Purchase #3	$56.52	5.711%	$59.7479	$59.75	$59.75	$59.70
Purchase #4	$207.32	7.199%	$222.245	$222.25	$222.25	$222.20
Purchase #5	$124.34	11.523%	$138.6677	$138.67	$138.65	$138.70
Purchase #6	$226.83	13.231%	$256.8419	$256.84	$256.85	$256.80
Purchase #7	$123.89	7.225%	$132.8411	$132.84	$132.85	$132.80
7 purchase totals =	$1,111.77		$1,231.3857	$1,231.39	$1,231.40	$1,231.30