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	$247.89	4.671%	$259.4689	$259.47	$259.45	$259.50
Purchase #2	$45.29	6.492%	$48.2302	$48.23	$48.25	$48.20
Purchase #3	$216.87	7.759%	$233.6969	$233.70	$233.70	$233.70
Purchase #4	$151.49	13.592%	$172.0805	$172.08	$172.10	$172.10
Purchase #5	$47.94	5.429%	$50.5427	$50.54	$50.55	$50.50
Purchase #6	$223.49	9.128%	$243.8902	$243.89	$243.90	$243.90
Purchase #7	$243.51	6.186%	$258.5735	$258.57	$258.55	$258.60
7 purchase totals =	$1,176.48		$1,266.4829	$1,266.48	$1,266.50	$1,266.50