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	$51.50	10.782%	$57.0527	$57.05	$57.05	$57.10
Purchase #2	$69.68	12.733%	$78.5524	$78.55	$78.55	$78.60
Purchase #3	$193.69	13.142%	$219.1447	$219.14	$219.15	$219.10
Purchase #4	$50.43	12.254%	$56.6097	$56.61	$56.60	$56.60
Purchase #5	$195.63	11.535%	$218.1959	$218.20	$218.20	$218.20
Purchase #6	$117.92	4.716%	$123.4811	$123.48	$123.50	$123.50
Purchase #7	$60.56	9.565%	$66.3526	$66.35	$66.35	$66.40
7 purchase totals =	$739.41		$819.3891	$819.38	$819.40	$819.50