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	$12.60	6.773%	$13.4534	$13.45	$13.45	$13.50
Purchase #2	$229.31	7.874%	$247.3659	$247.37	$247.35	$247.40
Purchase #3	$238.83	8.592%	$259.3503	$259.35	$259.35	$259.40
Purchase #4	$208.48	11.311%	$232.0612	$232.06	$232.05	$232.10
Purchase #5	$223.40	12.379%	$251.0547	$251.05	$251.05	$251.10
Purchase #6	$11.78	6.440%	$12.5386	$12.54	$12.55	$12.50
Purchase #7	$104.67	6.334%	$111.2998	$111.30	$111.30	$111.30
7 purchase totals =	$1,029.07		$1,127.1239	$1,127.12	$1,127.10	$1,127.30