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	$121.79	12.780%	$137.3548	$137.35	$137.35	$137.40
Purchase #2	$133.25	11.393%	$148.4312	$148.43	$148.45	$148.40
Purchase #3	$193.42	13.868%	$220.2435	$220.24	$220.25	$220.20
Purchase #4	$46.31	9.379%	$50.6534	$50.65	$50.65	$50.70
Purchase #5	$102.64	8.561%	$111.427	$111.43	$111.45	$111.40
Purchase #6	$151.37	5.444%	$159.6106	$159.61	$159.60	$159.60
Purchase #7	$175.36	11.836%	$196.1156	$196.12	$196.10	$196.10
7 purchase totals =	$924.14		$1,023.8361	$1,023.83	$1,023.85	$1,023.80