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	$39.99	8.679%	$43.4607	$43.46	$43.45	$43.50
Purchase #2	$223.46	5.770%	$236.3536	$236.35	$236.35	$236.40
Purchase #3	$123.71	11.397%	$137.8092	$137.81	$137.80	$137.80
Purchase #4	$150.71	3.167%	$155.483	$155.48	$155.50	$155.50
Purchase #5	$70.55	3.393%	$72.9438	$72.94	$72.95	$72.90
Purchase #6	$244.60	13.292%	$277.1122	$277.11	$277.10	$277.10
Purchase #7	$54.54	3.154%	$56.2602	$56.26	$56.25	$56.30
7 purchase totals =	$907.56		$979.4227	$979.41	$979.40	$979.50