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	$25.98	13.414%	$29.465	$29.47	$29.45	$29.50
Purchase #2	$70.95	11.175%	$78.8787	$78.88	$78.90	$78.90
Purchase #3	$128.65	9.743%	$141.1844	$141.18	$141.20	$141.20
Purchase #4	$144.94	12.171%	$162.5806	$162.58	$162.60	$162.60
Purchase #5	$232.86	10.111%	$256.4045	$256.40	$256.40	$256.40
Purchase #6	$38.75	4.254%	$40.3984	$40.40	$40.40	$40.40
Purchase #7	$8.89	8.517%	$9.6472	$9.65	$9.65	$9.60
7 purchase totals =	$651.02		$718.5588	$718.56	$718.60	$718.60