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	$247.46	4.772%	$259.2688	$259.27	$259.25	$259.30
Purchase #2	$240.87	6.842%	$257.3503	$257.35	$257.35	$257.40
Purchase #3	$118.79	5.639%	$125.4886	$125.49	$125.50	$125.50
Purchase #4	$107.32	13.601%	$121.9166	$121.92	$121.90	$121.90
Purchase #5	$217.62	4.503%	$227.4194	$227.42	$227.40	$227.40
Purchase #6	$35.91	13.863%	$40.8882	$40.89	$40.90	$40.90
Purchase #7	$41.52	10.536%	$45.8945	$45.89	$45.90	$45.90
7 purchase totals =	$1,009.49		$1,078.2264	$1,078.23	$1,078.20	$1,078.30