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	$76.33	5.531%	$80.5518	$80.55	$80.55	$80.60
Purchase #2	$40.34	11.309%	$44.9021	$44.90	$44.90	$44.90
Purchase #3	$86.99	13.347%	$98.6006	$98.60	$98.60	$98.60
Purchase #4	$167.37	6.622%	$178.4532	$178.45	$178.45	$178.50
Purchase #5	$102.93	8.677%	$111.8612	$111.86	$111.85	$111.90
Purchase #6	$42.48	11.839%	$47.5092	$47.51	$47.50	$47.50
Purchase #7	$223.39	13.250%	$252.9892	$252.99	$253.00	$253.00
7 purchase totals =	$739.83		$814.8673	$814.86	$814.85	$815.00