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	$48.44	13.562%	$55.0094	$55.01	$55.00	$55.00
Purchase #2	$39.47	7.810%	$42.5526	$42.55	$42.55	$42.60
Purchase #3	$159.43	8.126%	$172.3853	$172.39	$172.40	$172.40
Purchase #4	$39.56	9.667%	$43.3843	$43.38	$43.40	$43.40
Purchase #5	$118.45	6.597%	$126.2641	$126.26	$126.25	$126.30
Purchase #6	$225.85	6.520%	$240.5754	$240.58	$240.60	$240.60
Purchase #7	$231.55	3.677%	$240.0641	$240.06	$240.05	$240.10
7 purchase totals =	$862.75		$920.2352	$920.23	$920.25	$920.40