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	$27.31	4.360%	$28.5007	$28.50	$28.50	$28.50
Purchase #2	$236.75	11.359%	$263.6424	$263.64	$263.65	$263.60
Purchase #3	$131.42	5.778%	$139.0134	$139.01	$139.00	$139.00
Purchase #4	$186.51	5.514%	$196.7942	$196.79	$196.80	$196.80
Purchase #5	$153.68	3.235%	$158.6515	$158.65	$158.65	$158.70
Purchase #6	$227.52	13.192%	$257.5344	$257.53	$257.55	$257.50
Purchase #7	$24.30	11.588%	$27.1159	$27.12	$27.10	$27.10
7 purchase totals =	$987.49		$1,071.2525	$1,071.24	$1,071.25	$1,071.20