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	$138.38	8.760%	$150.5021	$150.50	$150.50	$150.50
Purchase #2	$234.56	12.433%	$263.7228	$263.72	$263.70	$263.70
Purchase #3	$185.56	11.324%	$206.5728	$206.57	$206.55	$206.60
Purchase #4	$105.27	10.642%	$116.4728	$116.47	$116.45	$116.50
Purchase #5	$39.38	3.648%	$40.8166	$40.82	$40.80	$40.80
Purchase #6	$20.44	9.856%	$22.4546	$22.45	$22.45	$22.50
Purchase #7	$129.41	10.646%	$143.187	$143.19	$143.20	$143.20
7 purchase totals =	$853.00		$943.7287	$943.72	$943.65	$943.80