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	$28.56	4.256%	$29.7755	$29.78	$29.80	$29.80
Purchase #2	$76.45	5.870%	$80.9376	$80.94	$80.95	$80.90
Purchase #3	$22.62	13.349%	$25.6395	$25.64	$25.65	$25.60
Purchase #4	$67.61	7.180%	$72.4644	$72.46	$72.45	$72.50
Purchase #5	$92.97	10.273%	$102.5208	$102.52	$102.50	$102.50
Purchase #6	$152.56	13.347%	$172.9222	$172.92	$172.90	$172.90
Purchase #7	$77.83	5.106%	$81.804	$81.80	$81.80	$81.80
7 purchase totals =	$518.60		$566.0640	$566.06	$566.05	$566.00