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	$250.86	3.422%	$259.4444	$259.44	$259.45	$259.40
Purchase #2	$116.62	10.357%	$128.6983	$128.70	$128.70	$128.70
Purchase #3	$133.85	3.476%	$138.5026	$138.50	$138.50	$138.50
Purchase #4	$117.42	11.625%	$131.0701	$131.07	$131.05	$131.10
Purchase #5	$69.26	13.190%	$78.3954	$78.40	$78.40	$78.40
Purchase #6	$206.78	5.321%	$217.7828	$217.78	$217.80	$217.80
Purchase #7	$153.54	7.560%	$165.1476	$165.15	$165.15	$165.10
7 purchase totals =	$1,048.33		$1,119.0412	$1,119.04	$1,119.05	$1,119.00