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	$37.56	6.600%	$40.039	$40.04	$40.05	$40.00
Purchase #2	$137.45	13.640%	$156.1982	$156.20	$156.20	$156.20
Purchase #3	$91.70	12.554%	$103.212	$103.21	$103.20	$103.20
Purchase #4	$34.62	8.586%	$37.5925	$37.59	$37.60	$37.60
Purchase #5	$200.53	9.258%	$219.0951	$219.10	$219.10	$219.10
Purchase #6	$43.79	5.261%	$46.0938	$46.09	$46.10	$46.10
Purchase #7	$158.50	13.260%	$179.5171	$179.52	$179.50	$179.50
7 purchase totals =	$704.15		$781.7477	$781.75	$781.75	$781.70