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	$234.55	13.144%	$265.3793	$265.38	$265.40	$265.40
Purchase #2	$126.93	4.175%	$132.2293	$132.23	$132.25	$132.20
Purchase #3	$116.37	5.571%	$122.853	$122.85	$122.85	$122.90
Purchase #4	$157.81	10.192%	$173.894	$173.89	$173.90	$173.90
Purchase #5	$100.61	11.258%	$111.9367	$111.94	$111.95	$111.90
Purchase #6	$26.56	8.350%	$28.7778	$28.78	$28.80	$28.80
Purchase #7	$73.27	6.832%	$78.2758	$78.28	$78.30	$78.30
7 purchase totals =	$836.10		$913.3459	$913.35	$913.45	$913.40