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	$235.33	10.291%	$259.5478	$259.55	$259.55	$259.50
Purchase #2	$165.48	12.759%	$186.5936	$186.59	$186.60	$186.60
Purchase #3	$247.90	8.722%	$269.5218	$269.52	$269.50	$269.50
Purchase #4	$167.42	8.730%	$182.0358	$182.04	$182.05	$182.00
Purchase #5	$117.87	10.296%	$130.0059	$130.01	$130.00	$130.00
Purchase #6	$131.88	12.826%	$148.7949	$148.79	$148.80	$148.80
Purchase #7	$145.39	12.845%	$164.0653	$164.07	$164.05	$164.10
7 purchase totals =	$1,211.27		$1,340.5651	$1,340.57	$1,340.55	$1,340.50