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	$37.33	12.533%	$42.0086	$42.01	$42.00	$42.00
Purchase #2	$119.48	10.455%	$131.9716	$131.97	$131.95	$132.00
Purchase #3	$155.26	7.437%	$166.8067	$166.81	$166.80	$166.80
Purchase #4	$47.26	12.523%	$53.1784	$53.18	$53.20	$53.20
Purchase #5	$58.98	7.307%	$63.2897	$63.29	$63.30	$63.30
Purchase #6	$48.40	4.616%	$50.6341	$50.63	$50.65	$50.60
Purchase #7	$37.46	13.782%	$42.6227	$42.62	$42.60	$42.60
7 purchase totals =	$504.17		$550.5118	$550.51	$550.50	$550.50