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	$123.68	13.842%	$140.7998	$140.80	$140.80	$140.80
Purchase #2	$168.89	3.218%	$174.3249	$174.32	$174.30	$174.30
Purchase #3	$74.85	8.836%	$81.4637	$81.46	$81.45	$81.50
Purchase #4	$211.48	9.178%	$230.8896	$230.89	$230.90	$230.90
Purchase #5	$64.25	13.578%	$72.9739	$72.97	$72.95	$73.00
Purchase #6	$19.83	3.706%	$20.5649	$20.56	$20.55	$20.60
Purchase #7	$51.60	7.241%	$55.3364	$55.34	$55.35	$55.30
7 purchase totals =	$714.58		$776.3532	$776.34	$776.30	$776.40