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	$48.39	6.657%	$51.6113	$51.61	$51.60	$51.60
Purchase #2	$81.55	9.814%	$89.5533	$89.55	$89.55	$89.60
Purchase #3	$74.92	13.517%	$85.0469	$85.05	$85.05	$85.00
Purchase #4	$144.54	3.829%	$150.0744	$150.07	$150.05	$150.10
Purchase #5	$237.56	10.606%	$262.7556	$262.76	$262.75	$262.80
Purchase #6	$186.87	10.379%	$206.2652	$206.27	$206.25	$206.30
Purchase #7	$116.83	11.448%	$130.2047	$130.20	$130.20	$130.20
7 purchase totals =	$890.66		$975.5114	$975.51	$975.45	$975.60