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	$64.64	12.273%	$72.5733	$72.57	$72.55	$72.60
Purchase #2	$86.76	3.591%	$89.8756	$89.88	$89.90	$89.90
Purchase #3	$63.52	4.589%	$66.4349	$66.43	$66.45	$66.40
Purchase #4	$149.46	12.218%	$167.721	$167.72	$167.70	$167.70
Purchase #5	$202.54	3.787%	$210.2102	$210.21	$210.20	$210.20
Purchase #6	$38.45	8.468%	$41.7059	$41.71	$41.70	$41.70
Purchase #7	$192.75	9.229%	$210.5389	$210.54	$210.55	$210.50
7 purchase totals =	$798.12		$859.0598	$859.06	$859.05	$859.00