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	$50.76	7.314%	$54.4726	$54.47	$54.45	$54.50
Purchase #2	$157.88	5.661%	$166.8176	$166.82	$166.80	$166.80
Purchase #3	$200.79	4.313%	$209.4501	$209.45	$209.45	$209.50
Purchase #4	$93.91	10.587%	$103.8523	$103.85	$103.85	$103.90
Purchase #5	$69.66	7.492%	$74.8789	$74.88	$74.90	$74.90
Purchase #6	$29.38	6.544%	$31.3026	$31.30	$31.30	$31.30
Purchase #7	$100.47	3.542%	$104.0286	$104.03	$104.05	$104.00
7 purchase totals =	$702.85		$744.8027	$744.80	$744.80	$744.90