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	$47.86	5.173%	$50.3358	$50.34	$50.35	$50.30
Purchase #2	$54.93	10.338%	$60.6087	$60.61	$60.60	$60.60
Purchase #3	$243.89	13.189%	$276.0567	$276.06	$276.05	$276.10
Purchase #4	$75.37	9.181%	$82.2897	$82.29	$82.30	$82.30
Purchase #5	$110.89	8.640%	$120.4709	$120.47	$120.45	$120.50
Purchase #6	$208.39	4.433%	$217.6279	$217.63	$217.65	$217.60
Purchase #7	$138.72	6.346%	$147.5232	$147.52	$147.50	$147.50
7 purchase totals =	$880.05		$954.9129	$954.92	$954.90	$954.90