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	$229.87	12.792%	$259.275	$259.28	$259.30	$259.30
Purchase #2	$53.27	4.429%	$55.6293	$55.63	$55.65	$55.60
Purchase #3	$40.66	6.381%	$43.2545	$43.25	$43.25	$43.30
Purchase #4	$54.51	9.495%	$59.6857	$59.69	$59.70	$59.70
Purchase #5	$179.51	12.872%	$202.6165	$202.62	$202.60	$202.60
Purchase #6	$11.86	13.126%	$13.4167	$13.42	$13.40	$13.40
Purchase #7	$128.98	6.127%	$136.8826	$136.88	$136.90	$136.90
7 purchase totals =	$698.66		$770.7603	$770.77	$770.80	$770.80