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	$247.40	13.179%	$280.0048	$280.00	$280.00	$280.00
Purchase #2	$180.79	5.516%	$190.7624	$190.76	$190.75	$190.80
Purchase #3	$204.77	12.249%	$229.8523	$229.85	$229.85	$229.90
Purchase #4	$80.46	13.536%	$91.3511	$91.35	$91.35	$91.40
Purchase #5	$78.29	13.420%	$88.7965	$88.80	$88.80	$88.80
Purchase #6	$75.34	10.196%	$83.0217	$83.02	$83.00	$83.00
Purchase #7	$100.71	4.536%	$105.2782	$105.28	$105.30	$105.30
7 purchase totals =	$967.76		$1,069.0670	$1,069.06	$1,069.05	$1,069.20