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	$247.31	5.416%	$260.7043	$260.70	$260.70	$260.70
Purchase #2	$128.33	8.595%	$139.36	$139.36	$139.35	$139.40
Purchase #3	$114.39	13.293%	$129.5959	$129.60	$129.60	$129.60
Purchase #4	$183.47	13.820%	$208.8256	$208.83	$208.85	$208.80
Purchase #5	$144.93	9.391%	$158.5404	$158.54	$158.55	$158.50
Purchase #6	$165.63	4.349%	$172.8332	$172.83	$172.85	$172.80
Purchase #7	$86.26	3.645%	$89.4042	$89.40	$89.40	$89.40
7 purchase totals =	$1,070.32		$1,159.2636	$1,159.26	$1,159.30	$1,159.20