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	$108.69	10.730%	$120.3524	$120.35	$120.35	$120.40
Purchase #2	$189.52	3.706%	$196.5436	$196.54	$196.55	$196.50
Purchase #3	$202.35	12.833%	$228.3176	$228.32	$228.30	$228.30
Purchase #4	$11.81	3.305%	$12.2003	$12.20	$12.20	$12.20
Purchase #5	$196.39	10.714%	$217.4312	$217.43	$217.45	$217.40
Purchase #6	$82.75	8.357%	$89.6654	$89.67	$89.65	$89.70
Purchase #7	$13.56	9.328%	$14.8249	$14.82	$14.80	$14.80
7 purchase totals =	$805.07		$879.3354	$879.33	$879.30	$879.30