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	$215.36	5.570%	$227.3556	$227.36	$227.35	$227.40
Purchase #2	$189.30	5.679%	$200.0503	$200.05	$200.05	$200.10
Purchase #3	$80.32	10.732%	$88.9399	$88.94	$88.95	$88.90
Purchase #4	$158.90	12.617%	$178.9484	$178.95	$178.95	$178.90
Purchase #5	$40.47	12.330%	$45.46	$45.46	$45.45	$45.50
Purchase #6	$46.98	13.159%	$53.1621	$53.16	$53.15	$53.20
Purchase #7	$12.43	12.366%	$13.9671	$13.97	$13.95	$14.00
7 purchase totals =	$743.76		$807.8834	$807.89	$807.85	$808.00