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	$246.62	4.790%	$258.4331	$258.43	$258.45	$258.40
Purchase #2	$171.39	10.805%	$189.9087	$189.91	$189.90	$189.90
Purchase #3	$36.90	8.724%	$40.1192	$40.12	$40.10	$40.10
Purchase #4	$121.39	3.689%	$125.8681	$125.87	$125.85	$125.90
Purchase #5	$115.31	13.265%	$130.6059	$130.61	$130.60	$130.60
Purchase #6	$176.39	7.163%	$189.0248	$189.02	$189.00	$189.00
Purchase #7	$72.54	13.204%	$82.1182	$82.12	$82.10	$82.10
7 purchase totals =	$940.54		$1,016.0780	$1,016.08	$1,016.00	$1,016.00