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	$246.28	4.124%	$256.4366	$256.44	$256.45	$256.40
Purchase #2	$6.69	4.364%	$6.982	$6.98	$7.00	$7.00
Purchase #3	$14.88	7.363%	$15.9756	$15.98	$16.00	$16.00
Purchase #4	$55.73	10.604%	$61.6396	$61.64	$61.65	$61.60
Purchase #5	$148.40	4.520%	$155.1077	$155.11	$155.10	$155.10
Purchase #6	$59.82	11.629%	$66.7765	$66.78	$66.80	$66.80
Purchase #7	$40.82	9.234%	$44.5893	$44.59	$44.60	$44.60
7 purchase totals =	$572.62		$607.5073	$607.52	$607.60	$607.50