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	$50.84	6.127%	$53.955	$53.96	$53.95	$54.00
Purchase #2	$132.66	6.748%	$141.6119	$141.61	$141.60	$141.60
Purchase #3	$178.87	8.658%	$194.3566	$194.36	$194.35	$194.40
Purchase #4	$111.32	7.244%	$119.384	$119.38	$119.40	$119.40
Purchase #5	$237.64	12.390%	$267.0836	$267.08	$267.10	$267.10
Purchase #6	$85.81	4.213%	$89.4252	$89.43	$89.45	$89.40
Purchase #7	$122.95	7.369%	$132.0102	$132.01	$132.00	$132.00
7 purchase totals =	$920.09		$997.8265	$997.83	$997.85	$997.90