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	$12.54	9.686%	$13.7546	$13.75	$13.75	$13.80
Purchase #2	$33.97	10.384%	$37.4974	$37.50	$37.50	$37.50
Purchase #3	$62.67	10.563%	$69.2898	$69.29	$69.30	$69.30
Purchase #4	$58.52	11.529%	$65.2668	$65.27	$65.25	$65.30
Purchase #5	$204.75	11.121%	$227.5202	$227.52	$227.50	$227.50
Purchase #6	$71.78	3.689%	$74.428	$74.43	$74.45	$74.40
Purchase #7	$13.26	4.307%	$13.8311	$13.83	$13.85	$13.80
7 purchase totals =	$457.49		$501.5879	$501.59	$501.60	$501.60