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	$239.53	3.442%	$247.7746	$247.77	$247.75	$247.80
Purchase #2	$105.83	10.710%	$117.1644	$117.16	$117.15	$117.20
Purchase #3	$69.50	13.617%	$78.9638	$78.96	$78.95	$79.00
Purchase #4	$6.33	9.846%	$6.9533	$6.95	$6.95	$7.00
Purchase #5	$226.83	5.314%	$238.8837	$238.88	$238.90	$238.90
Purchase #6	$15.39	6.806%	$16.4374	$16.44	$16.45	$16.40
Purchase #7	$122.59	3.866%	$127.3293	$127.33	$127.35	$127.30
7 purchase totals =	$786.00		$833.5065	$833.49	$833.50	$833.60