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	$14.78	12.106%	$16.5693	$16.57	$16.55	$16.60
Purchase #2	$90.65	6.112%	$96.1905	$96.19	$96.20	$96.20
Purchase #3	$105.54	12.685%	$118.9277	$118.93	$118.95	$118.90
Purchase #4	$213.49	13.673%	$242.6805	$242.68	$242.70	$242.70
Purchase #5	$36.73	3.400%	$37.9788	$37.98	$38.00	$38.00
Purchase #6	$74.54	10.697%	$82.5135	$82.51	$82.50	$82.50
Purchase #7	$85.72	11.513%	$95.5889	$95.59	$95.60	$95.60
7 purchase totals =	$621.45		$690.4492	$690.45	$690.50	$690.50