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	$59.87	8.370%	$64.8811	$64.88	$64.90	$64.90
Purchase #2	$176.62	11.610%	$197.1256	$197.13	$197.15	$197.10
Purchase #3	$159.53	3.188%	$164.6158	$164.62	$164.60	$164.60
Purchase #4	$156.66	9.417%	$171.4127	$171.41	$171.40	$171.40
Purchase #5	$32.72	4.789%	$34.287	$34.29	$34.30	$34.30
Purchase #6	$123.54	7.550%	$132.8673	$132.87	$132.85	$132.90
Purchase #7	$40.36	4.286%	$42.0898	$42.09	$42.10	$42.10
7 purchase totals =	$749.30		$807.2793	$807.29	$807.30	$807.30