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	$213.85	5.169%	$224.9039	$224.90	$224.90	$224.90
Purchase #2	$100.38	4.371%	$104.7676	$104.77	$104.75	$104.80
Purchase #3	$199.67	11.332%	$222.2966	$222.30	$222.30	$222.30
Purchase #4	$37.59	13.708%	$42.7428	$42.74	$42.75	$42.70
Purchase #5	$117.36	9.275%	$128.2451	$128.25	$128.25	$128.20
Purchase #6	$147.72	12.794%	$166.6193	$166.62	$166.60	$166.60
Purchase #7	$81.25	5.198%	$85.4734	$85.47	$85.45	$85.50
7 purchase totals =	$897.82		$975.0487	$975.05	$975.00	$975.00