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	$134.54	3.666%	$139.4722	$139.47	$139.45	$139.50
Purchase #2	$88.69	9.792%	$97.3745	$97.37	$97.35	$97.40
Purchase #3	$176.44	7.445%	$189.576	$189.58	$189.60	$189.60
Purchase #4	$142.52	4.114%	$148.3833	$148.38	$148.40	$148.40
Purchase #5	$107.96	3.646%	$111.8962	$111.90	$111.90	$111.90
Purchase #6	$47.68	11.746%	$53.2805	$53.28	$53.30	$53.30
Purchase #7	$226.39	10.293%	$249.6923	$249.69	$249.70	$249.70
7 purchase totals =	$924.22		$989.6750	$989.67	$989.70	$989.80