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	$111.73	5.850%	$118.2662	$118.27	$118.25	$118.30
Purchase #2	$91.96	9.769%	$100.9436	$100.94	$100.95	$100.90
Purchase #3	$119.91	9.567%	$131.3818	$131.38	$131.40	$131.40
Purchase #4	$188.68	10.438%	$208.3744	$208.37	$208.35	$208.40
Purchase #5	$181.29	10.211%	$199.8015	$199.80	$199.80	$199.80
Purchase #6	$105.58	6.728%	$112.6834	$112.68	$112.70	$112.70
Purchase #7	$6.43	9.630%	$7.0492	$7.05	$7.05	$7.00
7 purchase totals =	$805.58		$878.5001	$878.49	$878.50	$878.50