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	$145.37	9.104%	$158.6045	$158.60	$158.60	$158.60
Purchase #2	$57.72	3.280%	$59.6132	$59.61	$59.60	$59.60
Purchase #3	$242.70	12.851%	$273.8894	$273.89	$273.90	$273.90
Purchase #4	$148.67	11.682%	$166.0376	$166.04	$166.05	$166.00
Purchase #5	$227.72	12.624%	$256.4674	$256.47	$256.45	$256.50
Purchase #6	$134.35	7.217%	$144.046	$144.05	$144.05	$144.00
Purchase #7	$206.76	9.421%	$226.2389	$226.24	$226.25	$226.20
7 purchase totals =	$1,163.29		$1,284.8970	$1,284.90	$1,284.90	$1,284.80