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	$94.30	12.213%	$105.8169	$105.82	$105.80	$105.80
Purchase #2	$148.33	8.123%	$160.3788	$160.38	$160.40	$160.40
Purchase #3	$112.47	3.754%	$116.6921	$116.69	$116.70	$116.70
Purchase #4	$250.39	11.727%	$279.7532	$279.75	$279.75	$279.80
Purchase #5	$91.43	7.691%	$98.4619	$98.46	$98.45	$98.50
Purchase #6	$239.95	7.659%	$258.3278	$258.33	$258.35	$258.30
Purchase #7	$95.53	4.820%	$100.1345	$100.13	$100.15	$100.10
7 purchase totals =	$1,032.40		$1,119.5652	$1,119.56	$1,119.60	$1,119.60