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	$249.71	6.157%	$265.0846	$265.08	$265.10	$265.10
Purchase #2	$184.52	8.577%	$200.3463	$200.35	$200.35	$200.30
Purchase #3	$78.46	13.870%	$89.3424	$89.34	$89.35	$89.30
Purchase #4	$80.25	3.798%	$83.2979	$83.30	$83.30	$83.30
Purchase #5	$70.98	10.827%	$78.665	$78.67	$78.65	$78.70
Purchase #6	$122.79	10.473%	$135.6498	$135.65	$135.65	$135.60
Purchase #7	$11.57	9.722%	$12.6948	$12.69	$12.70	$12.70
7 purchase totals =	$798.28		$865.0808	$865.08	$865.10	$865.00