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	$227.57	5.240%	$239.4947	$239.49	$239.50	$239.50
Purchase #2	$90.77	9.327%	$99.2361	$99.24	$99.25	$99.20
Purchase #3	$108.83	13.211%	$123.2075	$123.21	$123.20	$123.20
Purchase #4	$18.69	10.536%	$20.6592	$20.66	$20.65	$20.70
Purchase #5	$213.82	3.397%	$221.0835	$221.08	$221.10	$221.10
Purchase #6	$240.97	7.728%	$259.5922	$259.59	$259.60	$259.60
Purchase #7	$82.57	4.385%	$86.1907	$86.19	$86.20	$86.20
7 purchase totals =	$983.22		$1,049.4639	$1,049.46	$1,049.50	$1,049.50