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	$212.59	7.289%	$228.0857	$228.09	$228.10	$228.10
Purchase #2	$34.58	8.818%	$37.6293	$37.63	$37.65	$37.60
Purchase #3	$228.50	5.617%	$241.3348	$241.33	$241.35	$241.30
Purchase #4	$39.93	6.627%	$42.5762	$42.58	$42.60	$42.60
Purchase #5	$37.61	11.679%	$42.0025	$42.00	$42.00	$42.00
Purchase #6	$221.47	4.874%	$232.2644	$232.26	$232.25	$232.30
Purchase #7	$137.44	12.533%	$154.6654	$154.67	$154.65	$154.70
7 purchase totals =	$912.12		$978.5583	$978.56	$978.60	$978.60