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	$19.56	9.489%	$21.416	$21.42	$21.40	$21.40
Purchase #2	$160.33	12.139%	$179.7925	$179.79	$179.80	$179.80
Purchase #3	$74.54	5.439%	$78.5942	$78.59	$78.60	$78.60
Purchase #4	$107.56	8.243%	$116.4262	$116.43	$116.45	$116.40
Purchase #5	$89.32	11.446%	$99.5436	$99.54	$99.55	$99.50
Purchase #6	$48.38	9.425%	$52.9398	$52.94	$52.95	$52.90
Purchase #7	$124.56	7.267%	$133.6118	$133.61	$133.60	$133.60
7 purchase totals =	$624.25		$682.3241	$682.32	$682.35	$682.20