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	$136.39	10.579%	$150.8187	$150.82	$150.80	$150.80
Purchase #2	$146.94	4.786%	$153.9725	$153.97	$153.95	$154.00
Purchase #3	$25.57	7.748%	$27.5512	$27.55	$27.55	$27.60
Purchase #4	$100.53	11.200%	$111.7894	$111.79	$111.80	$111.80
Purchase #5	$66.89	11.375%	$74.4987	$74.50	$74.50	$74.50
Purchase #6	$41.76	5.251%	$43.9528	$43.95	$43.95	$44.00
Purchase #7	$82.80	13.815%	$94.2388	$94.24	$94.25	$94.20
7 purchase totals =	$600.88		$656.8221	$656.82	$656.80	$656.90