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	$43.55	12.569%	$49.0238	$49.02	$49.00	$49.00
Purchase #2	$58.99	3.434%	$61.0157	$61.02	$61.00	$61.00
Purchase #3	$168.88	6.510%	$179.8741	$179.87	$179.85	$179.90
Purchase #4	$126.76	13.799%	$144.2516	$144.25	$144.25	$144.30
Purchase #5	$227.72	5.659%	$240.6067	$240.61	$240.60	$240.60
Purchase #6	$40.78	8.461%	$44.2304	$44.23	$44.25	$44.20
Purchase #7	$54.59	9.527%	$59.7908	$59.79	$59.80	$59.80
7 purchase totals =	$721.27		$778.7931	$778.79	$778.75	$778.80