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	$81.86	11.422%	$91.21	$91.21	$91.20	$91.20
Purchase #2	$12.43	8.474%	$13.4833	$13.48	$13.50	$13.50
Purchase #3	$54.71	9.565%	$59.943	$59.94	$59.95	$59.90
Purchase #4	$56.86	9.505%	$62.2645	$62.26	$62.25	$62.30
Purchase #5	$44.90	7.490%	$48.263	$48.26	$48.25	$48.30
Purchase #6	$245.36	7.150%	$262.9032	$262.90	$262.90	$262.90
Purchase #7	$37.65	6.482%	$40.0905	$40.09	$40.10	$40.10
7 purchase totals =	$533.77		$578.1575	$578.14	$578.15	$578.20