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	$24.99	11.317%	$27.8181	$27.82	$27.80	$27.80
Purchase #2	$158.61	11.143%	$176.2839	$176.28	$176.30	$176.30
Purchase #3	$27.68	7.808%	$29.8413	$29.84	$29.85	$29.80
Purchase #4	$115.88	13.671%	$131.722	$131.72	$131.70	$131.70
Purchase #5	$71.53	9.192%	$78.105	$78.11	$78.10	$78.10
Purchase #6	$155.89	13.115%	$176.335	$176.34	$176.35	$176.30
Purchase #7	$65.94	6.742%	$70.3857	$70.39	$70.40	$70.40
7 purchase totals =	$620.52		$690.4910	$690.50	$690.50	$690.40