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	$99.94	6.520%	$106.4561	$106.46	$106.45	$106.50
Purchase #2	$100.68	13.690%	$114.4631	$114.46	$114.45	$114.50
Purchase #3	$78.72	11.841%	$88.0412	$88.04	$88.05	$88.00
Purchase #4	$76.85	11.587%	$85.7546	$85.75	$85.75	$85.80
Purchase #5	$155.83	5.727%	$164.7544	$164.75	$164.75	$164.80
Purchase #6	$177.40	8.406%	$192.3122	$192.31	$192.30	$192.30
Purchase #7	$200.68	13.262%	$227.2942	$227.29	$227.30	$227.30
7 purchase totals =	$890.10		$979.0758	$979.06	$979.05	$979.20