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	$236.89	9.686%	$259.8352	$259.84	$259.85	$259.80
Purchase #2	$132.38	10.517%	$146.3024	$146.30	$146.30	$146.30
Purchase #3	$57.28	4.646%	$59.9412	$59.94	$59.95	$59.90
Purchase #4	$192.88	7.849%	$208.0192	$208.02	$208.00	$208.00
Purchase #5	$123.89	10.135%	$136.4463	$136.45	$136.45	$136.40
Purchase #6	$191.31	5.391%	$201.6235	$201.62	$201.60	$201.60
Purchase #7	$75.51	13.255%	$85.5189	$85.52	$85.50	$85.50
7 purchase totals =	$1,010.14		$1,097.6867	$1,097.69	$1,097.65	$1,097.50