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	$238.34	10.519%	$263.411	$263.41	$263.40	$263.40
Purchase #2	$182.43	7.692%	$196.4625	$196.46	$196.45	$196.50
Purchase #3	$207.43	8.177%	$224.3916	$224.39	$224.40	$224.40
Purchase #4	$5.50	13.638%	$6.2501	$6.25	$6.25	$6.30
Purchase #5	$119.43	9.755%	$131.0804	$131.08	$131.10	$131.10
Purchase #6	$95.78	5.572%	$101.1169	$101.12	$101.10	$101.10
Purchase #7	$35.25	5.249%	$37.1003	$37.10	$37.10	$37.10
7 purchase totals =	$884.16		$959.8128	$959.81	$959.80	$959.90