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	$22.43	5.194%	$23.595	$23.60	$23.60	$23.60
Purchase #2	$53.57	10.223%	$59.0465	$59.05	$59.05	$59.00
Purchase #3	$137.76	4.697%	$144.2306	$144.23	$144.25	$144.20
Purchase #4	$76.42	10.615%	$84.532	$84.53	$84.55	$84.50
Purchase #5	$33.89	13.633%	$38.5102	$38.51	$38.50	$38.50
Purchase #6	$136.27	8.818%	$148.2863	$148.29	$148.30	$148.30
Purchase #7	$176.51	3.370%	$182.4584	$182.46	$182.45	$182.50
7 purchase totals =	$636.85		$680.6590	$680.67	$680.70	$680.60