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	$132.86	7.765%	$143.1766	$143.18	$143.20	$143.20
Purchase #2	$166.35	12.629%	$187.3583	$187.36	$187.35	$187.40
Purchase #3	$128.51	10.445%	$141.9329	$141.93	$141.95	$141.90
Purchase #4	$83.81	6.700%	$89.4253	$89.43	$89.45	$89.40
Purchase #5	$67.98	3.767%	$70.5408	$70.54	$70.55	$70.50
Purchase #6	$183.30	9.309%	$200.3634	$200.36	$200.35	$200.40
Purchase #7	$12.86	7.455%	$13.8187	$13.82	$13.80	$13.80
7 purchase totals =	$775.67		$846.6160	$846.62	$846.65	$846.60