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	$53.32	11.754%	$59.5872	$59.59	$59.60	$59.60
Purchase #2	$51.93	10.840%	$57.5592	$57.56	$57.55	$57.60
Purchase #3	$136.83	10.718%	$151.4954	$151.50	$151.50	$151.50
Purchase #4	$85.27	9.409%	$93.2931	$93.29	$93.30	$93.30
Purchase #5	$149.31	7.131%	$159.9573	$159.96	$159.95	$160.00
Purchase #6	$20.78	5.446%	$21.9117	$21.91	$21.90	$21.90
Purchase #7	$18.37	12.157%	$20.6032	$20.60	$20.60	$20.60
7 purchase totals =	$515.81		$564.4071	$564.41	$564.40	$564.50