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	$128.78	10.688%	$142.544	$142.54	$142.55	$142.50
Purchase #2	$39.39	13.400%	$44.6683	$44.67	$44.65	$44.70
Purchase #3	$37.87	13.573%	$43.0101	$43.01	$43.00	$43.00
Purchase #4	$29.52	4.338%	$30.8006	$30.80	$30.80	$30.80
Purchase #5	$72.90	6.338%	$77.5204	$77.52	$77.50	$77.50
Purchase #6	$248.97	10.239%	$274.462	$274.46	$274.45	$274.50
Purchase #7	$157.88	5.352%	$166.3297	$166.33	$166.35	$166.30
7 purchase totals =	$715.31		$779.3351	$779.33	$779.30	$779.30